Effects of kibble characteristics on feeding

behaviour in cats

Agata Teresa Kozuchowicz

August, 2018

Wageningen University and Research:

Student registration number: 870914-471-050

Course code: ANU-80430

Aarhus University

Student registration number: 201604359

Course code: 210122U004

Supervisors:

Dr.ir. Thomas van der Poel

Associate Professor at Animal Nutrition Group

Department of Animal Sciences

Wageningen University and Research, the Netherlands

Dr.ir. Guido Bosch

Researcher at Animal Nutrition Group

Department of Animal Sciences

Wageningen University and Research, the Netherlands

Dr Helle Nygaard Lærke

Senior Researcher at Molecular Nutrition and Reproduction Group

Department of Science and Technology

Aarhus University, Denmark

Copyright

No part of this publication may be reproduced and/or published in any form or by any means,

electronic, mechanical, photocopying, recording or otherwise, without prior written permission

of the head of the Animal Nutrition Group of Wageningen University, The Netherlands.

Abstract

Research on the effect of extrusion on nutrients (proteins, starch and lipids) and texture

preferences of pet food and cat feeding behaviour are often held by the manufactures, but most

of the time are confidential. Consequently, there is only a limited public knowledge about the

influence of the different variables of kibble characteristics on the feline ingestion behaviour.

Studies in other species have shown that eating/feeding behaviour influences health to a

significant extent. Therefore, the primary aim of this project was to find out how the physical

and chemical properties of dry foods, translate into the way cats eat these foods. The secondary

aim was, to evaluate the precision of available texture measurement methodologies. Based on

shape and macronutrients level, 18 commercially available dry cat food kibbles were selected.

Texture parameters were measured by a texture analyser (Instron 3366) with four different

probes: platen, blade, cone and cat model. Additionally, hardness was evaluated by Kahl pellet

hardness tester (Amadeus Kahl Nachf 2057) and Soltac tablet hardness tester (MT 50). From

the 18 foods, twelve foods were chosen for in vivo ingestion behaviour evaluation based on

their physical (shape, hardness, surface area) and chemical characteristics. Each food was tested

in a randomised pattern, by eight domestic European shorthair cats. During the tests, cats were

recorded by a Go Pro camera (JVC Everio, Model GZ-MS150HE). The time of ingestion [s]

and a number of chews [rate per min (rpm)] were obtained by analysing obtained recordings.

The chemical composition did not explain the variation found in measured hardness values

among kibbles irrespective of the method of measurement (P>0.1). Ingestion time increased

with 0.93 s per %-unit of crude protein (P=0.013) and decreased with 10.69 s per kg of hardness

measured with the cat model probe on the Instron (P<0.001). Shape influenced biting rate

(P<0.001) with cats biting most on turbine-shaped kibbles (9.7±1.1; P=0.001) and triangle-

shaped kibbles (3.2±1.1) tended to be eaten with fewer bites than disc-shaped kibbles (5.4±1.1,

P=0.065). The biting rate decreased with 0.65 units per %-unit of crude protein (P<0.001). The

biting rate increased with 1.83 rpm per kg of hardness measured with the cat model on the

Instron (P=0.048). The lowest variability of results provides blade probe and the highest the cat

model probe. The outcomes give an inside of how cat food kibble characteristics are related to

eating behaviour and introduce precision of several texture evaluation methods.

Keywords: cat food texture; kibble hardness; biting rate; ingestion speed; chewiness

Table of content

1 Introduction ......................................................................................................................... 1

2 Literature review ................................................................................................................. 2

2.1 Texture parameters of food and methods of evaluation .............................................. 2

2.2 Texture Testing in the Pet Food Industry .................................................................... 6

2.3 Influence of macronutrient composition on kibble texture and palatability ................ 8

2.3 Feeding behaviour of cats .......................................................................................... 14

2.4 Influence of kibble physical characteristics on feeding behaviour ............................ 15

3 Hypothesis and research questions ................................................................................... 17

4 Material and methods ........................................................................................................ 18

4.1 Food selection ............................................................................................................ 18

4.2 Physical characteristics .............................................................................................. 19

4.3 Eating behaviour in vivo test ..................................................................................... 22

4.4 Calculations and statistical analysis ........................................................................... 23

5 Results ............................................................................................................................... 24

6 Discussion ......................................................................................................................... 28

7 Conclusion ........................................................................................................................ 31

8 Recommendations ............................................................................................................. 31

9 Literature references: ........................................................................................................ 32

Appendix I. Total number of texture measurements made with Instron .................................. 36

Appendix II. Correction formula for cat model probe ............................................................. 39

Appendix III. Detailed intake protocol ..................................................................................... 40

Appendix IV. Hardness mean ± SD, and CV, its average and range of investigated kibbles .. 58

Appendix V. Ingredients of experimental foods ...................................................................... 59

Appendix VI. Additional data .................................................................................................. 61

1

1 Introduction

Cats have become one of the most popular companion animals in the Western World. The

pet food companies aim to produce foods supporting long-term wellbeing due to increasing

cat lifetime. Expansion of the feline life and change in habits contribute to certain health

issues, such as dental problems, obesity and impaired functionality of inner organs (Shreve

et al., 2017). Pet food manufacturers try to come across those issues by improving nutritional

composition and texture properties of produced foods (Bradshaw et al., 2012).

Extruded cat food is a complete, easy to apply, safe and relatively cheap food with a long

shelf life. Therefore, kibbles are the most popular type of food offered to cats, and the

demand for it is still growing. In 2016 the global production of extruded pet food reached 25

million tons, and in the 2017 28 million tons (Pet Food Industry, 2018). Kibbles differ a lot

in nutrient composition and physical characteristics from the food available for felines in

(Deursen, 2017). In pet food science, ingestion behaviour and food preferences are referred

to palatability, what is usually described as mouth-feel (hardness, shape, surface area, etc.),

taste and aroma. The chemical and physical properties of kibbles are influenced by the

quality and kind of used ingredients, nutrient composition and processing conditions (Éles

et al., 2014). Research on the effect of extrusion on nutrients (proteins, starch and lipids) and

texture preferences of pet food and cat feeding behaviour are often held by the manufactures,

but most of the time are confidential. Therefore, there is only a limited public knowledge

about the influence of the different variables of kibble characteristics on the feline ingestion

behaviour. Studies in other species have shown that eating/feeding behaviour influences

health to a significant extent. For example obesity research in humans suggests that multiple

chews before swallowing decrease size of eaten meal lowering at the same time eating rate

and overall energy consumption, which helps to avoid digestion disorders and control weight

(Shah et al. 2014, Zhu et al., 2014). Furthermore, veterinarian publications stress out that the

prevalence of periodontal diseases in pets ranges from 60% to more than 80% (Niemiec,

2010). Tartar development on the teeth provides an excellent environment for the growth of

microorganisms, which causes unpleasant breath, inflammation and development of diseases

(Éles et al., 2014). Bailoni et al. (2005) suggested, that hardness of kibbles can be negatively

correlated with tartar formation and that certain physical properties of kibbles can benefit

the oral health of pets.

The introduction is followed by the literature review that describes the texture characteristics

of food and methods of their evaluation, the influence of inclusion of macronutrients on

texture properties of kibbles and feeding behaviour in cats. The next part introduces the

hypothesis and research questions. Thereafter, the methodology of kibble selection, the

texture measurements methods and the in vivo investigation of feeding behaviour are

explained. Next two chapters introduce and discuss the results, what is followed by the

conclusion and recommendations for further studies. Later, the list of publications referred

in this report is presented. Lastly, the appendix with additional information on performed

research is included.

2

2 Literature review

2.1 Texture parameters of food and methods of evaluation

Texture is an important characteristic of all extruded food products. Several researchers

measured the texture of dry pet food using instrumental analysis (e.g. Bailoni et al., 2005, Figge

et al., 2011, Éles et al. 2014, Monti et al., 2016), but there is no agreement regarding

methodology and which terms should be used, or if those terms are correlated with sensory

texture perceived by cat or dog.

According to Szczesniak’s initial research (1963), food texture is a sensory manifestation of

structure and the way in which the structure responds to the forces applied. It depicts the

junction of the mechanical (e.g. hardness, fracturability, chewiness), geometrical (e.g. shape,

size, particle orientation inside the food) and superficial (features related to the perception of

moisture or fat content) characteristics of a food sample (Table 1). Those parameters are

determined by the response of tested food to the applied stress of teeth, tongue and pallet while

the ingestion process (sensory investigation) is imitated by various texture objective tests

(mechanical investigation).

Table 1. Classification of textural characteristics*

Mechanical characteristics

Primary parameters Secondary parameters Popular term

Hardness Soft → Firm → Hard

Cohesiveness Brittleness/ Fracturability Crumbly → Crunchy → Brittle Chewiness Tender → Chewy → Tough Gumminess Short → Mealy → Pasty/Gummy

Viscosity Thin → Viscous

Springiness/Elasticity Plastic → Elastics

Adhesiveness Sticky → Tacky / Gooey

Geometrical characteristics

Class Examples

Particle size and shape Gritty, grainy, coarse, etc.

Particle shape and orientation Fibrous, cellular, crystalline, etc.

Other parameters

Primary parameters Secondary parameters Popular terms

Moisture content Dry → Moist → Wet → Watery

Fat content Oiliness Oily Greasiness Greasy

Szczesniak et al., 1963

Within the instrumental test machines, texturometers (Figure 1a) mimic the mastication

conditions in the mouth cavity and the obtained texture profile of a sample is correlated with

sensory evaluations of texture by humans (Szczesniak et al., 1963). This is why texture profile

analysers have been broadly used to evaluate the texture in food and later on in feed industry.

The technique of the texture profile analysis (TPA) contains several steps. First, the food sample

(standard bite-size) is placed on the base plate, then the platen probe compress and decompress

the specimen twice (Figure 1b; Bourne et al., 2002). The result of a measurement is a force-

time curve that depicts the texture characteristics of a sample with several parameters. A typical

TPA force-time curve is shown in Figure 2 (Bourne, 2002).

3

Figure 1. a) Example of a Texture Analyzer (TA.XT Plus, Texture Technologies, Scarsdale,

NY); b) Schema of the two-compressions test for the regular TPA: A- downstroke actions

during first and second compression, B-upstroke actions during the first and second

compression (Bourne, 2002)

Figure 2. TPA force-time curve obtained during double compression test with platen probe

(Bourne, 2002)

b a

moving platen

food sample

base

first bite

second bite

a A

A B

B

4

Figure 3. TPA of a kibble during a single compression with platen probe. Hardness (N) is

defined as the maximum achieved force during compression, fracturability (N) is the maximal

force of the first peak, chewability is the calculated positive area under the force curve, and

adhesiveness is the calculated negative area under the force curve (internal data, WUR 2018).

Civille et al. (1973) concluded that hardness is the force necessary to achieve deformation of a

food sample during mastication to compress a food between molars (Table 2). It is expressed

in kilogram (kg) or Newton (N). In the force-time curve created during the TPA test in the peak

of power reached during the first compression.

Cohesiveness is the force of internal bonds (structural integrity) that allows to withstands

compressive or tensile stress (Table 2). A product with a high cohesion is more tolerant to the

handling stress (packaging and transportation).

Elasticity (springiness) was described by Civille et al. (1973) as the recovered distance of food

sample of its original shape after deforming power is removed (Table 2). It is the height that

the sample retrieves during the time between the end of the first cycle and the start of the second

cycle in a double compression test.

Szczesniak and Civile defined adhesiveness as the adherence of the food to the palate and teeth,

or as the force needed to overcome the adherence between the surface of food and mouth cavity,

that the sample has contact with (teeth, palate, tongue). As the sensory feature, adhesives is

defined as the necessary force needed to remove the food material that adheres to the mouth

cavity (mainly the palate) during the usual ingestion process (Table 2, Szczesniak et al., 1963;

Civille et al., 1973). It is the negative part for the first chew, representing the effort to pull the

probe of the sample after compression. Inelastic foods are never adhesive (Novaković et al.,

2017).

5

Brittleness (fracturability) described as the force necessary to fracture, crumble or shatter of the

sample (Table 2) and is related to the hardness and cohesiveness of the food (Szczesniak et al.,

1963; Civille et al., 1973). Furthermore, Solà-Oriol et al. (2009) connected fracturability with

fragility – the time needed to achieve the maximum force while chewing. Novaković et al.

(2017) pointed out that fragile materials (like for instance kibbles) have low cohesiveness and

those foods can simply rupture. Therefore, the first peak might be interpreted as hardness, if

only one single peak appears at the force-time curve.

Table 2. Definitions of texture mechanical parameters*

Physical Sensory

Primary

properties

Hardness Force necessary to attain a given deformation

Force required to compress a substance

between molar teeth (in the case of solids)

or between tongue and palate (in the case

of semi-solids).

Cohesiveness Extent to which a material can be deformed

before it ruptures

Degree to which a substance is compressed

between the teeth before it breaks

Springiness

Rate at which a deformed material goes back to

its undeformed condition after the deforming

force is removed

Degree to which a product returns to its

original shape once it has been compressed

between the teeth

Adhesiveness

Work necessary to overcome the attractive

forces between the surface of the food and the

surface of the other materials with which the

food comes in contact

Force required to remove the material that

adheres to the mouth (generally the palate)

during the normal eating process

Secondary

properties

Fracturability

Force with which a material fractures a product

of the high degree of hardness and low degree

of cohesiveness

Force with which a sample crumbles,

cracks, or shatters

Chewiness

Energy required to masticate a solid food to a

state ready for swallowing: a product of

hardness, cohesiveness and springiness

Length of time [s] required to masticate the

sample, at a constant rate of force

application, to reduce it to a consistency

suitable for swallowing

Gumminess

Energy required to disintegrate a semi-solid

food to a state ready for swallowing a product

of a low degree of hardness and a high degree

of cohesiveness

Denseness that persists throughout

mastication; the energy required to

disintegrate a semi-solid food to a state

ready for swallowing

*Civille et al., 1973

Chewability (chewiness) is understood in several ways. Friedman et al. (1963) defined it in

respect to physical properties, as the “energy [J] required to masticate a solid food to a state

ready for swallowing: a product of hardness, cohesiveness and springiness”. In the sensory

approach, the same authors described chewability as “the length of time [s] needed to masticate

a sample, at a constant rate of force application, to reduce it, to a consistency suitable for

swallowing.” Trinh et al. (2012) described an alternative to the definition of chewability

proposed by Friedman at al. (1963). The researchers analysed products with a very fast rate of

6

breakdown (what could relate to crispiness) and with a very slow rate of breakdown (what could

relate to toughness). They concluded that chewability is “the energy required to disintegrate the

food until it is ready to swallow” and it is a sum of energies expanded in each successive bite.

Paula et al. (2014) interpreted chewiness as “the number of chews necessary for food to be

swallowed” while investigating the texture properties of extruded snacks. Different approaches

to measuring chewability were introduced by Ambros et al. (1998) and Solà-Oriol et al. (2009).

Ambros et al. (1998) discussed the advantages of axial above radial breaking forces in

investigating the chewiness of tablets by using the three-point flexure tensile strength test. Solà-

Oriol et al. (2009) expressed chewiness (kg*mm) as the positive area under the curve during

evaluation of extruded food for swine in one compression test (Figure 3).

Gumminess is understood as the energy obligatory to disintegrate a semi-solid food sample to

a state allowing swallow (Table 2). It is a characteristic only for foods with low hardness and

calculated by multiplication of hardness and cohesiveness (Civille et al., 1973, Novaković et

al., 2017).

2.2 Texture Testing in the Pet Food Industry

According to information provided by Food Technology Corporation. The food industry

improved the basic TPA developed by Szczesniak et. al. (1963). Next, to the original platen

probe, it is proposed, to use different kinds of probes (cylinders, cones, knives etc.).

Consequently, in pet food industry apart from the basic compression TPA, there are four

additional methods of mechanical testing for sensory texture attributes: penetration and

puncture tests, shear tests, tension tests and snap, bend and break tests.

Penetration and puncture tests are conducted to obtain measures of hardness, bite force of a

sample and firmness. Penetration can be done with cone or needle probes (Figure 4a,b). A

variation of this method is a multiple point penetration test to measure firmness in canned wet

food.

Shear tests can measure the average hardness, tenderness, bite strength, and cook quality by

cutting the sample with a blade (Figure 4c,d) that mimic the action applied by the edge of teeth.

Tension tests (Figure 4e) help to assess the elasticity of chewy treats. During tension evaluation,

the texture analyser pulls or stretches the test sample, to measure the elasticity and the ultimate

strength of the product.

The Snap, Bend and Break method is a three-point bend test (figure 4f) is suitable for measuring

brittleness or flexibility of bar-shaped treats and their bend strength. According to (Bourne et

al., 2002) above methods should not be considered as the texture profile analyse developed by

Szczesniak et. al. (1963).

7

Figure 4. Examples of probes for texture analyser tasting in feed industry: a) 30° cone; b) needle

ø 3 mm, 25 mm long; c) knife blade with 45° chisel end; d) incisor knife blade; e) tensile grips;

f) three-point bend rig (TTC, 2018)

There are also several other methods for fast evaluation of texture properties. For instance, Kahl

pallet hardness tester was the first practical instrument that was widely used in the feed industry.

In this device, the specimen (single pellet) is placed between two bars and compressed at a

constant load rate until it brakes, and the breaking force recorded. Twelve measurements are

performed from which the highest and the lowest are skipped. The mean of 10 repetitions gives

a value called ‘Kahl-hardness’ (Van der Poel et al., 1996, Figure 5a). Another alternative for

testing hardness of dry pet food could be instruments used in pharmaceutical industry for

evaluating the hardness of tablets such as Monsanto tester, Strong-cobb tester, Pfizer tester or

Schleuniger tester.

The Monsanto Hardness Tester (Figure 5b) was developed in the 1979 year by Monsanto

Research in Miamisburg, OH, in the USA. The tester consists of a barrel with a compressible

spring held between two plungers. The lower plunger is put in contact with the specimen, and

a zero reading is taken. The upper plunger is then pushed against a spring by turning a threaded

screw until the sample breaks. When a spring is compressed, a pointer moves along a gauge in

the barrel to indicate the applied force. The breaking force is recorded and a zero reading is

deducted from it (McCallum et al., 1955).

The Strong-cobb tester (Figure 5c) is built out of a piston activated by pumping a lever arm,

which presses an anvil against a stationary platform with hydraulic pressure. The fracturing

force of a specimen is seen at the hydraulic gauge.

8

The Pfizer tester (Figure 5d) works on the same principle as a pair of pliers. When the plier's

grips are squeezed, the specimen is compressed between a holding anvil and a piston attached

to a reading gauge. The dial indicator stays at the reading where the specimen breaks and it

returns to zero after pushing the reset button (Fairchild et al., 1961).

The Schleuniger Pharmaton tester (Figure 5e) works in a horizontal position. An anvil,

controlled by an electrical motor, pushes on a specimen at statically increasing force until the

sample breaks. The braking force is taken from a scale indicator (Pharmatron, 2018).

Figure 5. Examples of hardness testers in feed and pharmaceutical industry: a) Kahl Pellet

Hardness Tester, model K3175-0000 (Industrial World, 2018); b) Monsanto Hardness Tester

(Farmalabor Tech, 2018); c) Strong Cobb Tablet Hardness Tester, model Sht 17 (Tim Trade,

2018); d) Pfizer tester (Pharmacy Instruments India, 2018); e) Schleuniger Pharmaton tester,

model MT50 (Cobra, 2018)

2.3 Influence of macronutrient composition on kibble texture and palatability

Extrusion

Extrusion is a complex process involving various operations, such as mixing, conveying,

heating, kneading, shearing, and shaping. Firstly, the raw materials are ground to the desired

size of particles and mixed. Then, the dry powder is passed through a pre-conditioner, in which

wet ingredients (meat, fat and water) are added. Afterwards, hot steam is injected to the mash

what induces the cooking process and then the mixture is pressed through an extruder (Tran,

2008). The extruder is built of a stationary barrel with a tightly fitting rotating screw inside,

ending with a die. The extruder's rotating screw forces the mash through the die and cut by

rotating blades to the required length. The kibbles expand, release moisture and heat. In the end,

they are cooled, dried and coated with palatability enhancer (Ye et al., 2018). The thermal

energy and the shearing effect created in the extrusion process, provoke physicochemical

9

reactions in the dough. The mash ingredients undergo numerous order-disorder changes,

gelatinization of starch, denaturation of protein and form variety complexes between them and

other nutrients. The characteristics of raw materials and the processing parameters determine

the nutritional value, structure and texture features of extruded foods (Tran, 2008). In general,

every food consists of protein, fats, carbohydrates (starch and fibres), and water.

Starch

Starch is made of two α-glucan polymer molecules, amylopectin and amylose. Native starch is

stored in plants in the form of partially crystalline granules characteristic for every species. In

an extruder, starch granules are processed with water. They hydrate, swell, break down and

degrade, changing at the end into a viscoelastic mass, which expands right after leaving the die

(Moraru et al., 2003). The expansion ratio of starch during the extrusion process and its

influence on extrudate physical properties have been studied in many research studies. In

general, the higher inclusion of starch, the higher expansion of kibbles, but the results are

inconsistent in obtained expansion degree of extrudates. Ye et al. (2018) concluded, that the

differences are due to the specific structure of different starch sources, characteristics of other

raw materials, and the interactions of starch with them, as well as the inconsistency in

processing conditions.

Figure 6. Scheme of the changes in starch granules during extrusion (Ye et al., 2018)

Commercially available foods for companion animals contain a high level of starch (Hewson-

Hughes et al. 2013). Domestic animals, like herbivores, are used to high levels and complex in

structure. Data in feline behavioural studies signify, that there is a ceiling amount (300 kJ) of

carbohydrates that cat can efficiently ingest per day and higher inclusion will reduce food intake

(Hewson-Hughes et al., 2013).

10

Protein

The protein inclusion of any pet food is the most nutritionally important and most expensive

constituent of the four major nutrients. The most desirable protein sources are those which

contain the essential amino acids profile required by the animal (Willard, 2003).

During extrusion, proteins undergo

many structural changes. They unfold,

realign, hydrolyse, denature and react

with other mash constituents. The

higher addition of protein, the more

intensive cross-linking between them

and starches, which results in the

higher rigidity of kibbles (Onwulata et

al., 2001). Depending on protein

source, concentration and its

processing before extrusion, created

complexes differ in expansion degree.

In extruded foods, protein inclusion is

normally lower than starch, which

favours expansion, crispness, and

increases bulk density (Day et al., 2013). The above theory is supported by research of

Onwulata et al. (2001) and Allan et al. (2007). Onwulata concluded that inclusion of whey

protein concentrate (250g/kg) or sweet whey solids (500 g/kg) to cornmeal flour, significantly

decreases (p < 0.05) the expansion index and increases the hardness of extrudates. Allan et al.

(2007) tested 3 different levels (16, 32 and 40%) of whey protein. The results clearly showed,

that the higher the inclusion of protein, the lower expansion of the extruded product (Figure 7).

Furthermore, scientific investigations conducted by SPF Diana Pet Food concluded that higher

inclusion of poultry meal in a food led to harder kibbles (Table 3, Fournier et. al., 2013).

Unfortunately, the method of texture measurements used in this research is not described.

Table 3. Impact of protein inclusion on the rigidity of kibbles*

Protein inclusion [%] Rigidity [N/mm]

25 22

35 36

40 49

Fournier et. al., 2013

Figure 7. Expansion of corn extrudates with different

level of whey protein (16% on the left, 32% in the

middle and 40% on the right, Allen et. al., 2007).

11

Fat

In the pet food industry, fat is added to the formulation as a lubricant, as an energy and essential

fatty acids source, and as an enhancer of palatability. The higher the inclusion of fat during

extrusion, the better lubrication. Fat inclusion reduces friction between the dough and barrel as

well as between the dough and screw elements resulting in lower feed temperature.

Furthermore, fat protects the starch granules from severe mechanical shear stress and reduce

their mechanical breakdown. Above factors significantly reduce the degree of starch

gelatinization and in turn expansion of kibbles (Colonna et al., 1983, Biliaderis et al., 1986,

Camire et al., 1990). This is clearly illustrated by Lin et al. (1997) in a study where the inclusion

of 7.5% of animal fat lowered the temperature in the barrel from 168°C to 136 °C. This

consequently reduced the degree of starch gelatinization from 100% (when no fat was added)

to 61% (Table 4). Another process that limits starch gelatinisation degree in the extruder is the

formation of starch-fat complexes. However, animal fats (poultry, pork and beef tallow), used

in dry pet food production contain mainly triglycerides. Triglycerides, due to their bulky size,

complex with starch to a very limited extent (Mercier et at., 1980). Therefore, the latter is

considered to have a minor effect on kibble texture characteristics.

Table 4. The influence of animal fat (poultry fat and beef tallow) inclusion on the degree of

starch gelatinisation*

Fat content (g/kg) Product temperature (°C) Degree of starch gelatinization (%)

0 168 100

25 156 99

50 142 88

75 136 61

*Lin et al., 1997

Coating extrudates with aromatized fat increase energy content, improve palatability and

surface structure of kibble. The optimal moisture content before the coating is 60 g/kg (Tran,

2008). The extrudates with low density and low moisture can absorb more aromatized fat thus

the aroma can penetrate deeper into and enhance kibble palatability. Lin et al. (1998) noticed

that higher inclusion of fat in dog dry food lowered rancidity (lipid oxidation) during a long

time storing (14 months). This is explained by the change in the texture of kibbles with higher

fat inclusion. Those extrudates were characterized by lower porosity and decreased the surface

area exposed to the air what reduced lipid oxidation.

12

Fibre

According to Monti et al. (2016), kibble characteristics are significantly impacted by the type

and particle size of the used fibre. The inclusion of fibre decreases the level of starch

gelatinisation, decreasing in turn expansion and reinforcing kibble structure (Robin et al., 2012).

However the mood of action of insoluble and soluble fibre fractions is different (Brennan et al.,

2008). Insoluble fibres, like for instance guava fibre, sugarcane or wheat bran, at a high

inclusion level increase the energy required to extrude the feed and by this reduce cooking of

starch. Above is proved by the research of Monti et. al. (2016) who investigated how the

increased inclusion of guava fibre (0-12%) in the formula affect the macrostructure of kibbles.

They concluded that different fibre inclusions significantly (p<0.001) affect kibble

characteristics, where the higher inclusion of guava fibre the lower starch gelatinisation degree

and radial expansion rate as well as increased cutting force (Table 5).

Table 5. The influence of different inclusion of guava fibre on starch gelatinisation degree,

radial expansion rate and cutting force*

inclusion of guava fibre

0% 3% 6% 12%

Starch gelatinization (%) 92.8 91.1 90.5 88.3

Radial expansion rate 4.1 3.9 3.5 3.2

Cutting force (kg.f) 2.4 2.9 3.1 3.4

*Monti et al., 2016

The main effect of higher inclusion of soluble fibre fractions in formulas is the increased water

absorption. When water is restricted, there is less starch degradation and gelatinisation during

extrusion (Dale et al., 2003). Furthermore, complex formation between starch and cellulose

molecules might alter the solubility of the paste and influence the texture properties. This

process is different for every individual mixture of used ingredients (native characteristics of

starch and fibres) in the formula, and there are no general conclusions on the mode of action

and effects on texture (Chinnaswamy et al., 1991, Robin et al., 2012).

Fibre, next to protein helps in regulation satiety in cats. Replacing protein with a source of

soluble and fermentable fibre in a food lowers the rate of gastric emptying. This helps to

increase the feeling of satiety in cats, which in turn limits the voluntary energy consumption

(Table 6, Biourge et al., 2014).

Table 6. The influence of crude protein and dietary fibre inclusion on daily energy intake in

cats feed ad libitum*

Crude protein [%] Dietary fibre [%] Daily energy intake (kcal/kg BW)

Food 1 41 16 43.1

Food 2 48 10 48.9

Food 3 36 21 39.6

*Biourge et al., 2014

13

Moisture

Water has two main functions in food processing. It plays an important role as a solvent and as

a lubricator. Mathew et al. (1999) described a positive correlation between increasing the mash

moisture in the range of 9.5-13.5% and expansion of pet food extrudate. Also, increasing

moisture level during extrusion causes higher nutrient retention and higher durability of

extrudate, what reduce the number of fines and generation of waste (Sørensen, 2003). Extruded

cat food has a moisture level between 200-300 g/kg (Lankhorst et al., 2007). In order to improve

it texture properties, palatability and extend shelf life the water content must be decreased.

Therefore, after extrusion kibbles are dried.

Fournier (2013) tested 150 cat food kibbles produced from the same formula, but with different

water content. Extrudates, after coating with poultry fat (6%), were treated with either dry

palatability enhancer, liquid palatability enhancer, or with a mixture of both. In the end, the

moisture of produced kibbles was varying from 4 to 10%. They concluded that cats detect a

significant difference when the moisture content between two kibbles exceeds 0.75% and that

they prefer dryer products (Figure 8a). Furthermore, they analysed the texture of investigated

kibbles and noticed that a rigidity of the extrudates was negatively correlated with water content

(Figure 8b). Moreover, SPF Diana Pet Food suggests, that the moisture level impacts the release

of volatile compounds, what might further alter the palatability (Fournier et. al., 2013).

However, it is important to point out, that in the mentioned above report, neither the results are

clearly introduced, nor the methodology of texture measurement is described.

Figure 8. a) The relation between the different water content in kibbles on the consumption

ratio b) The relation between the different water content in kibbles and rigidity (Fournier et.

al., 2013).

14

2.3 Feeding behaviour of cats

Cats are opportunistic eaters, and their feeding pattern depends on the food availability, whether

hunted, scavenged or delivered by the owner. When the difficulty of getting food increases, the

meal size increases as well. In general, cats do not follow a circadian rhythm. They prefer to

eat small, similar in size meals throughout the day and night. (Kane et al., 1987). Cats regulate

their energy intake not by reducing the number of meals, but by decreasing the content of each

meal. The way, in which the meal size and the break between meals are controlled, is not yet

completely understood (Bradshaw et al., 2012).

Cats are considered to be true carnivores. Throughout evolution, the feline diet has been based

on animal tissues, which determines their unique nutritional requirements. Therefore, their

metabolism is adapted to a high protein and low carbohydrate food. Dissimilar to other

mammals, feline saliva does not contain amylase. Cats also lack a functional Tas1r2 receptor

and cannot taste sugars, but in turn, they are very good at differencing the taste of amino acids.

Cats have 30 teeth (12 incisors, 4 canines, 10 premolars and 4 molars, Figure 9). Feline teeth

and mouth are small. Their jaw joints do not move laterally but only vertically, which is meant

to kill and hold a prey while hunting, rather than grind or chew (Hewson-Hughes et al., 2011).

Food, except the mechanical breakdown in the mouth, is also moistened with saliva in order to

lubricate the bolus to facilitate swallowing and further digestion.

Figure 9. Anatomy of the jaw of cats (Nutrition, 1997)

15

2.4 Influence of kibble physical characteristics on feeding behaviour

According to Horwitz et al. (2010) investigation, cats grab kibbles one by one with the incisors

or tongue, crash them with premolars and rapidly swallow. They observed that cats take kibbles

in three different ways: labial (without the use of tongue), supralingual (with the use of the

ventral side of tongue) or sublingual (with the use of the dorsal side of the tongue, Figure 10).

Figure 10. Prehension methods of kibbles (Horwitz et al., 2010)

Royal Canin Research Centre also had a close look at the eating customs of domestic cats. They

investigated the habits of 8 adult cats housed together in one group. They were fed ad libitum

with the same dry food. Every animal was equipped with an electronic chip and followed in

real time. This enabled recording of each cat consumption profile without any disturbance for

over 17 days. The rate of eating varied between 1.8 to 18 g/min and was on average was 4.7

g/min. The meal size ranged from 2.8 to 17.4 g with a mean of 6.0 g/meal. The duration of

eating a single meal differed from 36 s to 4.07 min and on average was 1.55 min. The break

between meals took on average 18.09 min (4-34 min). Overall, cats had 9.7 (1-19) meals and

ate 55.2 g (10-100g) of food a day (Royal Canin Research Centre, internal data, cited by

Horwitz et al., 2014).

Van Deursen (2017) concluded that the chewing and biting rate of dry foods is significantly

lower (p<0.001), than when consuming a prey (mice, birds or rodents, Table 6). The researcher

explored differences in cat eating behaviour when consuming different kinds of prey, wet food

and kibbles by analysing video recordings of eating cats on YouTube (www.youtube.com).

This was explained, by the more structural, and bigger in size natural sources of cat food. The

above implies that the pattern of feeding behaviour depends on the kind of meal offered.

Table 7. Average chewing + biting rate of cats eating mice, birds, lagomorphs and rodents,

kibbles and wet food (each n=25)*

Food type Chewing and bating [rpm]

Mice 53.47±2.94

Birds 50.75±2.98

Lagomorphs and rodents 59.72±2.86

Kibbles 44.66±3.22

Wet food 31.18±3.11

*Deursen, 2017

16

Ruth Van Koppen (2017) observed the difference in feeding behaviour of cats when consuming

normal and palatable food. Sixteen cats were recorded twice during consumption of each food.

The recordings were analyzed for the effects of palatability, sex and interactions between those

factors, on the eating behaviour. The chewing varied between 96.8 and 111.7 rpm but neither

the addition of taste enhancer nor the sex had a significant influence on the speed of ingestion

(p>0.1). Those results are in agreement with Becques et. al. (2014) who investigated the

influence of palatability of the same food with different taste enhancers applied on the kibbles.

One part of the food was coated with super-premium hydrolysate with a poultry basis and the

second part-less palatable with normal hydrolysate with a viscera basis. The speed of

consumption varied between 3.4 to 5.3 g/min and did not differ significantly between

investigated diets (p>0.1) but overall, cats consumed significantly more kibbles with more

palatable enhancer than the regular one.

Another crucial research concerning the influence of kibble shape and texture on palatability

was performed by the AFB International Research Group and presented by Figge at Petfood

Forum (2011). According to the results (Table 8), the main palatability driver was the shape of

the kibble. The most palatable shape within the exanimated group was a disc with mid-ranged

hardness, then the cross (the hardest kibble) followed by triangle-shaped kibbles and triangle

with a hole (lowest hardness score). The cylinder was the thickest kibble with moderate

hardness and was the least preferred one by cats. An unmentioned component in this research

is the surface area of kibbles that could influence introduced results because the bigger surface

area the larger contact area covered with flavour enhancer.

Table 8. The influence of kibble physical characteristics on preference in feline*

Texture Preference

Shape Moisture

[%]

Diameter

[cm]

Thickness

[cm]

Hardness

^ [kg]

7.40 0.36 0.19 5.39 >a = >

a >

a

8.59 0.54 0.18 8.08 < a

> a

> > a

8.59 0.45 0.18 7.06 = < a

= >

6.96 0.41 0.20 2.48 >

a = =

> a

8.58 0.32 0.39 4.23 < a

< a

< < a

*Figge et al., 2011; ^ measurements done with the Instron Texture Analyser (3342) and Cherry Pitter Needle

probe; a: p < 0.05

17

3 Hypothesis and research questions

Based on the literature review above, it can be deducted that research concerning the influence

of chemical and physical characteristic on the way of ingestion by cats is limited. Therefore,

the primary aim of this project is to determine how the physical and chemical properties of

foods translate into the way cats eat these foods. In addition, as various texture measurement

methodologies are available, the secondary aim is to evaluate the extent of accuracy of available

texture measurement methodologies. The specific aims are to study:

I. How physical and chemical properties of foods translate into the way cats eat these foods

Research questions:

1. How does the crude chemical composition (moisture, protein, fat, fibre and starch relate

to the physical properties of cat food kibbles (hardness)?

It is expected that a higher level of protein, fibre and lower starch, as well as moisture

content, will increase the hardness of kibbles.

2. How do the physical (hardness, shape) and chemical (protein, fat, fibre) characteristics

of kibbles relate to the ingestion of the kibbles in cats (chewing rate, time of ingestion)?

It is expected, that hardness will be positively related with chewing rate, and that disc and

triangle shaped kibbles will be eaten at a slower rate than the turbine shaped.

A higher protein, fat and fibre level is expected to lead to fewer chews and shorter time for

ingestion.

II. To evaluate the precision of available texture measurement methodologies

Research questions:

1. Which of available hardness tests (MT50, Instron, Kahl) is the most precise when

evaluating cat food kibbles?

It is expected that the MT 50 is the most precise method, i.e. yields lowest variation among

technical replicates.

2. What is the variability in Instron texture analysis outcomes when using different probes

(plate, blade, cone, cat jaw model)?

The highest variability is expected in measurements done with the platen probe.

18

4 Material and methods

4.1 Food selection

Commercially available cat food kibbles selected to this experiment are presented in Table 9.

They are chosen in respect to shape and chemical composition. Three kinds of shapes were

selected (disc, turbine, triangle). Chemical composition varied for crude protein (<30% and

>40%), crude fat (<12% and > 21%) and crude fibre (<2% and >5%), with n=3 foods (1 disc,

1 turbine, 1 triangle) for each level and percentages on dry matter basis.

Chosen kibbles are bought in the online stores (www.zooplus.nl, www.brekz.nl) and in the local

supermarket Albert Heijn (Wageningen, the Netherlands). The selected food and their chemical

compositions are shown in Table 9.

Table 9. The shape and labelled moisture and chemical composition (% of dry matter) of

selected dry cat food kibbles

Food Kind Shape* Moisture^ CP CF Crude fibre NFE Ash

1

high in protein

O 6 44.15 17.55 2.98 30.53 4.79

2 Y 43.48 13.04 2.72 31.52 9.24

3 Δ 6 45.74 6.38 3.72 36.38 7.77

4

low in protein

O 26.09 21.74 3.80 44.02 4.35

5 Y 32.61 16.30 2.61 41.20 7.28

6 Δ 7 29.03 13.98 4.30 44.84 7.85

7

high in fat

O 35.54 22.50 1.41 34.78 5.76

8 Y 38.04 21.74 2.72 30.43 7.07

9 Δ 7 35.48 24.73 5.38 26.56 7.85

10

low in fat

O 35.87 10.87 5.43 39.13 8.70

11 Y 38.04 10.87 6.52 36.96 7.61

12 Δ 34.02 8.91 8.26 42.83 5.98

13

high in fibre

O 34.78 11.96 5.98 39.13 7.00

14 Y 43.01 10.75 8.17 30.32 7.74

15 Δ 7 36.96 14.13 6.52 34.24 8.15

16

low in fibre

O 33.12 18.41 1.27 41.80 5.40

17 Y 5.5 35.48 23.66 1.72 31.18 7.96

18 Δ 38.80 13.15 1.41 38.91 7.72

* O disc-shaped kibbles; Y turbine-shaped kibbles; Δ triangle-shaped kibbles

^ Moisture levels were specified only on few labels of experimental foods. Therefore, for calculation

of dry matter, it was assumed that the moisture level is equal 8% (average moisture of dry cat food,

Evertse, 2017)

Abbreviations: NFE, Nitrogen-free extract; CP, crude protein; CF, crude fat;

19

4.2 Physical characteristics

Surface area, thinness and weight

Thinness, length, width and height were measured with the use of a calliper. Fifteen randomly

chosen kibbles from each food were measured and the average was calculated. The thickness

is the height of the kibble in the middle of the kibble. The surface area (SA) was estimated for

every shape separately using a shape-specific formula (Table 10). It is a total SA of a sum of

the SA of the top, the SA of the bottom and the SA of the kibble side/sides. Weight was assessed

with the use of a laboratory scale with 0.01g accuracy by weighing 20 randomly selected,

unbroken kibbles of each food.

Table 10. Equations used to calculate the SA of differently shaped kibbles

Kibble shape Surface area estimation

O 2πr2+2πrt

Y 2*3bc+6b+6c+2(c2√3/4)

Δ 2*1/2ah+3at

SA of the top, SA of the bottom and the SA of the

side:

π – 3.1415

r – radius of the circle (in the disc-shaped kibbles)

t – thickness of the kibble

h – height of the triangle (in the triangle shaped

kibbles)

a – length of the side (in the triangle and turbine

shaped kibble

b – length of the arm (in the turbine shaped kibbles)

c – vertical thickness of the arm (in the turbine

shaped kibbles)

Texture parameters

Texture parameters assessment was done by the Instron Texture Analyser 3366 by a one cycle

test. The samples were examined with four different probes: platen (ø 5.6 cm), blade (0.3 mm),

cone (30°) and cat model (Figure 11). The platen probe was attached to the crosshead in a

regular way. The blade, cone and cat model probes were combined with a buckle that was

connected with the crosshead (Figure 11b). The cat model probe was adapted with artificial

cheek and lounge made from play dough to prevent sliding kibbles out of the teeth during the

test. The kibbles were always placed on the top of the last premolar and molar teeth on the

bottom of the right jaw (Figure 11e). The screw speed was 3.5 mm/s and preload 0.1 N. The

compression level was always 100% except for the platen probe, where it was reduced to 75%.

Kibbles from every food were chosen randomly. The raw data were recorded by Bluehill 2

software and transferred to Excel 2016 (Microsoft). Based on those datasets, the texture

parameters were calculated for every specimen manually. Due to practical difficulties during

the tests (e.g. kibble sliding out of the probe, unreadable graphs), some of the tests had to be

repeated. The complete number of tests and the reasons for excluding them from the research

are described in Appendix 1.

20

Figure 11. Instron Texture Analyser 3366 a) with the platen probe connected with the regular

crosshead, b) with the cat model probe installed to buckle combined with the crosshead, c) blade

probe, d) cone probe, e) kibble placed on the top of the last premolar and molar teeth on the

bottom right jaw in the cat model probe adapted with artificial cheek and tongue made from

play dough.

Seven successful replicates from every food were selected to further evaluation. The texture

parameters were derived or calculated as follows: Hardness (kg) was defined as the maximal

force that the kibble achieves during the compression of the probe. It is the highest peak in the

force-time curve (Figure 12a, Friedman et al., 1963, Szczesniak et al., 2002) Chewiness

(kg*mm) was interpreted as the positive area under the curve (area 1. Figure 12a, Solà-Oriol et

al., 2009). The area under the curve was obtained by the trapezoid rule. The area under the

curve was divided into a series of trapezoids and the sum of all areas of those trapezoids gave

the total area under the curve (Cruz-Uribe et al., 2002). Since the applied force was moved

horizontally 5 cm on the arm of the cat model, the actual force applied on the specimen had to

be adjusted (Archimedes law of the lever, described by Vince, 1797). Therefore, the obtained

with cat model probe results were multiplied by 1.77 (Appendix 2, Vince, 1797).

21

Figure 12 a) General force time curve from TPA single compression dry test on a single kibble

(internal data, WUR 2018); b) Horizontal shift of 5 cm of applied force on the cat model probe

arm.

Since two more methods were available, hardness was also measured by Kahl pellet hardness

tester (Amadeus Kahl Nachf 2057 Reinbek, Figure 13a) and Soltac Multi-Test Tablet Hardness

Tester (MT50, Figure 13b). Twelve randomly selected kibbles from every food were

individually tested. Every specimen was placed between two bars. During the test with Soltac,

the kibbles were held with tweezers to ensure proper position of the specimen (Figure 13b).

The force applied on the kibble was increasing statically until the kibble cracked. The applied

force at the moment of breaking the kibble was recorded. The highest and the lowest value were

skipped and the hardness was an average of 10 measurements (Ton Nu, 2009).

Figure 13. Hardness measurement by a) Kahl pallet hardness tester and b) by Soltac MT 50

22

4.3 Eating behaviour in vivo test

From the 18 foods, twelve foods were chosen for in vivo evaluation by cats. The foods were

selected based on the results obtained in a first part of the experiment (SA, thinness, hardness),

shape and chemical composition. Eight domestic European shorthair cats (four males, four

females) experienced with different kinds of dry foods were used in this study. Before the

observation started cats were gradually adapted (4 days) from the wet to the familiar dry food

(Perfect Fit Indoor, Mars Petcare, Verden, Germany). No changes were made to the housing

condition of the cats. The study lasted for 2 weeks. During this time, 4 rounds were conducted

of which the last one was a reserve round, where unsuccessful measurements from the previous

three rounds were repeated. Round 1 to 3 consisted of one adaptation day followed by one test

day. In round 4 the adaptation day was skipped. Rest days were included between the rounds

with 1 day between rounds 1 and 2 and rounds 3 and 4 and 2 days between rounds 2 and 3. The

adaptation and testing days followed the same pattern. At 8.00 h, all cats received 20% of the

daily portion of the familiar dry food in their individual feeding cages (1.00 x 0.74 x 1.74 m).

They were given 15 min for consuming the morning meal. Four food ingestion tests were

performed on each day for each cat. During each test, every the cats had 10 min time to consume

5 g of food in the individual feeding-cage. During the tests, eating behaviour was recorded by

a Go Pro camera (JVC Everio, Model GZ-MS150HE). Two cats were observed at the same

time (male in cage A and female in cage B). The first couple were starting at 10.00 h, the second

at 10.15 h, the third at 10.30 h and the fourth at 10.45 h. Cats had 2 h break between the tests

and return to their normal group room for the break time. The tests were finished no later than

16.55 h (Table 11).

Table 11. Cat feeding plan with experimental foods during adaptation and test days with an

indication of placing cats in the individual feeding cages.

round

1

cat (nr) in

feeding cage

(A or B)

round

2

cat (nr) in

feeding cage

(A or B)

round

3

cat (nr) in

feeding cage

(A or B)

round

4

cat (nr) in

feeding cage

(A or B)

A B A B A B A B

10.00 h 1 2 12.00 h 1 2 14.00 h 1 2 16.00 h 1 2

10.15 h 3 4 12.15 h 3 4 14.15 h 3 4 16.15 h 3 4

10.30 h 5 6 12.30 h 5 6 14.30 h 5 6 16.30 h 5 6

10.45 h 7 8 12.45 h 7 8 14.45 h 7 8 16.45 h 7 8

At 17.00 h, all cats were fed with the rest of their daily portion of their regular dry food corrected

for the energy intake during the tests. Order of testing the foods was random (Appendix III,

Attachment 2). The food was placed in a circle of one layer of kibbles in the corner of a cutting

board with a rough surface, which encouraged cats to sit in the desired position during the test

(Figure 14). In addition, because the break between tests was just 5 min, it was easier to

completely dry only the corner of the cutting board instead of the whole surface.

23

Figure 14. a) Example picture from obtained recordings; b) set up of a camera and a cutting

board in the experimental cage.

The detailed in vivo protocol with cat food set up, plan of the trial and report are included in

Appendix 3. The time of ingestion [s] and a number of chews [rate per min (rpm)] were obtained

by analysing recordings with the Movies & TV Microsoft Cooperation program and voice

monitoring headphones (Sennheiser HD 215). The crack of a braking kibble between the teeth

was assumed as a chew.

4.4 Calculations and statistical analysis

Descriptive statistics (mean value, standard deviation (SD), coefficient variation (CV) of each

tested food were calculated with the use of IBM SPSS Statistics software. Multiple regression

models (Model 1: relation between crude chemical composition and texture parameters; Model

2: relation between the crude chemical composition, physical kibble characteristics and

ingestion behaviour such as chewing/biting rate and ingestion speed) and post-hoc test (shape

vs biting rate) with exclusion of extraordinary data points (>mean+2SD and mean-2SD>) were

done using the SAS software (SAS 9.4, SAS Inst. Inc., Cary, NC, USA).

24

5 Results

Relation between the crude chemical composition and the physical properties of cat food

kibbles

The crude chemical composition of experimental foods varied between 26.09 and 45.74%, 6.38

and 24.73%, 1.27 and 8.26%, and between 27.41 and 45.69% for protein, fat, fibre and NFE

respectively (Table 9). Moisture was not part of the data set, as it was not declared on 12 out of

18 labels. Multiple regression was therefore performed without this factor. The outcomes of the

multiple regression analyses of hardness as measured with the Kahl test and with the cat model

on the Instron, as well as the chewiness obtained with cat model probe, are shown in Table 12.

The chemical components did not explain the variation found in measured hardness values

among kibbles irrespective of the method of measurement (P=0.890, P=0.935 and P=0.250

respectively).

Table 12. The relation between crude chemical composition and texture (hardness and

chewiness).

Parameter Estimates±SE

R2 P-value

Intercept CP CF Crude fibre NFE

Hardness

Kahl -44.0±114.4 0.61±1.23 0.63±1.23 0.96±1.39 0.51±1.25 0.083 0.890

Cat model -18.9±31.20 0.22±0.34 0.25±0.33 0.31±0.38 0.23±0.34 0.062 0.935

Chewiness

Cat model 37.44±34.50 0.45±0.36 0.32±0.39 0.47±0.37 0.47±0.37 0.340 0.250

Abbreviations: CP, crude protein; CF, crude fat; NFE, nitrogen-free extract

25

Relation between cat food kibble characteristics and ingestion

The relation between physical (hardness, weight, shape), as well as chemical (protein, fat, fibre)

characteristics of kibbles and the ingestion of the kibbles in cats (chewing rate, time for

ingestion), are presented in Table 13. Ingestion time increased with 0.93 s per %-unit of crude

protein (P=0.013) and decreased with 10.69 s per kg of hardness measured with the cat model

probe on the Instron (P<0.001). Crude fibre content tended to impact ingestion time with 1.30

s per %-unit (P=0.052). Other factors in the model did not significantly impact ingestion time

(P>0.10). Shape influenced biting rate (P<0.001) with cats biting most on turbine-shaped

kibbles (9.7±1.1; P=0.001, post hoc analysis) and triangle-shaped kibbles (3.2±1.1) tended to

be eaten with fewer bites than disc-shaped kibbles (5.4±1.1, P=0.065). The biting rate decreased

with 0.65 units per %-unit crude of protein (P<0.001). The biting rate increased with 1.83 rpm

per kg of hardness measured with the cat model on the Instron (P=0.048). Other factors in the

model did not significantly relate to biting rate (P>0.10).

Table 13. The relation between cat food kibble characteristics and ingestion

Effect Ingestion time P-value Bite rate P-value

Intercept 27.8±19.14 29.47±6.16

Shape

Disc 4.54±3.83

0.184

-4.28±1.25

<0.001 Triangle -1.99±3.37 -6.46±1.23

Turbine 0 0

Kibble weight 41.89±30.00 0.167 10.31±9.76 0.295

CP 0.93±0.36 0.013 -0.65±0.12 <0.001

CF 0.35±0.40 0.379 -0.19±0.13 0.139

Crude fibre 1.30±0.66 0.052 -0.13±0.22 0.558

Hardness-Cat model -10.69±2.78 <0.001 1.83±0.91 0.048

Abbreviations: CP, crude protein; CF, crude fat

26

Precision of available hardness tests (Kahl, Soltac, Instron) when evaluating cat food

kibbles

The measurements of hardness varied between the investigated foods from 4.29±0.52 to

16.4±1.47 kg for Kahl hardness tester, between 2.61±0.40 to 8.66±0.79 kg for Soltac and

between 8.22±1.94 and 68.6±12.32 kg when using Instron with platen probe for evaluation

(Table 14). The coefficient of variance (CV, %) results were in the range from 8 5 to 28%, 9%

32% and from 9% to 32 % for Kahl, Soltac and Instron with platen probe. The average equalled

15%, 17% and 21% respectively. Based on these data, Kahl hardness tester appears to be the

most precise method when evaluating the hardness of cat food kibbles and Instron platen gives

less precise outcomes than Soltac.

Table 14. Hardness mean ± SD, and CV, its average and range of investigated kibbles when

evaluated with Kahl, Soltac and Instron with platen probe

Food Kahl* Soltac* Instron platen^

Mean±SD CV [%] Mean±SD CV [%] Mean±SD CV [%]

1 12.83±2.68 21 5.88±1.48 25 14.73±3.79 26

2 10.25±1.31 13 3.517±1.12 32 12.73±1.74 14

3 4.29±0.52 12 4.23±0.65 15 68.6±12.32 18

4 8.31±1.68 20 4.25±0.45 10 19.07±6.18 32

5 8.42±2.34 28 5.15±1.42 28 11.79±3.07 26

6 11.63±1.75 15 6.41±0.70 11 13.16±2.13 16

7 14.23±2.24 16 5.75±1.39 24 17.99±4.44 25

8 4.44±0.35 8 2.61±0.40 15 8.22±1.94 24

9 16.4±1.47 9 8.66±0.79 9 24.12±6.18 26

10 12.42±1.12 9 6.38±0.76 12 15.48±1.94 13

11 15.9±2.13 13 7.07±0.88 13 23.66±5.09 21

12 8.44±1.06 13 6.82±0.66 1 23.39±7.42 32

13 13.69±1.38 10 6.23±1.40 23 36.08±3.30 9

14 11.18±2.15 19 6.88±1.00 14 12.43±1.32 11

15 5.44±0.91 17 3.92±0.55 14 8.53±1.40 16

16 7.94±1.01 13 4.8±0.96 20 13.55±2.16 16

17 10.9±1.36 12 5.15±0.94 18 15.14±3.31 22

18 8.95±2.4 27 6.38±1.12 18 14.92±3.98 27

Average 15 17 21

Range 8-28 9-32 9-32

* based on 12 replicate measurements with the omission of lowest and highest value (Ton Nu, 2009);

^ based on 7 replicate measurements (Ton Nu, 2009)

27

The variability in Instron texture analysis outcomes when using different probes (platen,

blade, cone, cat model)

The hardness values varied between the investigated foods between 8.22±1.94 and 68.6±12.32

kg when using Instron with platen probe, from 3.59±0.65 to 6.74±0.77 kg for blade probe,

between 1.85±0.37 and 17.91±4.41 kg with cone probe and between 1.40±0.53 and 5.43±0.77

kg when using Instron with platen probe (Table 15). The average coefficient of variance (CV,

%) were: 21% in the range from 9% to 32%, 19% in a range from 15% to 29%, 20% in a range

4% to 38% and 27% in a range from 11% to 43% for the platen, blade, cone and cat model

probes, respectively. These findings suggest that the lowest variability of results was provided

by the blade probe and the highest with the cat model probe. The platen probe is less precise

than when using the cone model probe.

Table 15. Hardness mean ± SD, and CV, its average and range of investigated kibbles when

using different probes for evaluation Instron probe

Food Platen Blade Cone Cat model

Mean±SD CV [%] Mean±SD CV [%] Mean±SD CV [%] Mean±SD CV [%]

1 14.73±3.79 26 5.98±0.89 15 3.38±0.99 29 3.45±1.49 43

2 12.73±1.74 14 3.59±0.65 18 2.84±0.29 1 1.69±0.38 23

3 68.6±12.32 18 4.05±1.16 29 5.37±0.24 4 5.43±0.77 14

4 19.07±6.18 32 3.67±0.64 18 1.91±0.21 11 2.12±0.54 26

5 11.79±3.07 26 5.21±0.84 16 3.71±0.97 26 2.28±0.82 36

6 13.16±2.13 16 5.23±1.04 2 3.56±0.55 15 3.64±1.05 29

7 17.99±4.44 25 4.64±0.74 16 17.91±4.41 25 4.48±0.75 17

8 8.22±1.94 24 3.03±0.94 31 1.85±0.37 20 1.40±0.53 38

9 24.12±6.18 26 6.74±0.77 11 4.44±0.78 18 4.54±1.94 43

10 15.48±1.94 13 6.17±0.84 14 2.90±0.36 12 3.59±0.54 15

11 23.66±5.09 21 6.54±0.95 14 3.83±0.60 16 3.34±0.71 21

12 23.39±7.42 32 5.28±1.03 19 3.29±0.39 12 2.65±0.3 11

13 36.08±3.30 9 4.70±1.38 29 3.56±0.92 26 3.13±0.39 12

14 12.43±1.32 11 5.53±0.82 15 2.89±0.68 24 2.61±0.34 13

15 8.53±1.40 16 3.14±0.51 16 1.95±0.74 38 2.07±0.78 38

16 13.55±2.16 16 3.53±0.72 2 2.64±0.77 29 2.70±0.95 35

17 15.14±3.31 22 4.21±1.04 25 2.98±0.88 30 1.93±0.76 39

18 14.92±3.98 27 6.45±1.22 19 4.31±1.41 20 3.09±0.99 32

Average 21 19 20 27

Range 9-32 15-29 4-38 11-43

28

6 Discussion

Although feline nutrition has been studied in depth by the industry, little is known about the

eating behaviour of dry cat food. Research in other species showed that the ingestion behaviour

influence health in many aspects. By finding a way to increase the chewing rate in cats, we

might reduce the problem of feline overeating and decrease plague development on their teeth.

Kibbles are the base of feline diet and therefore, this investigation focused on the associations

between the chemical and physical characteristics of cat food kibbles and feline ingestion

behaviour, as well as the evaluation of precision of several available texture assessment

methods.

Relation between the crude chemical composition and the physical properties of cat food

kibbles

Even though the experimental foods were selected in a wide range of macronutrients, the crude

chemical composition, seemed to not relate to the physical characteristics investigated in our

research. These results are in disagreement with our expectations. Earlier research showed that

higher inclusion of protein and fibre decrease expansion degree and increases the hardness of

extrudates (Onwulata et al., 2001, Allen et al. 2007, Fournier et. al., 2013, Monti et al., 2016).

Onwulata et. al. (2001) observed that addition 500g/kg of whey protein concentrate to the mash

significantly increased breaking strength index (BSI) from 3.8 N/mm (when no whey protein

concentrate was added) to 11.7 N/mm (P<0.01). A similar pattern was observed when the

inclusion of sweet whey solids was increased from 250 to 500 g/kg. The BSI increased from

5.9 to 9.8 N/mm (P<0.01) respectively. Onwulata et al. (2001) defined the BSI as hardness (N)

measured by texture analyser with Warner–Bratzler shear cell probe, divided by the diameter

of the extrudate (mm). Likewise, Fournier et. al. (2013) concluded that higher inclusion of

poultry meal in a dry pet food elevates rigidity. The rigidity of kibbles equalled 22 N/mm when

the inclusion of protein was 25% and increased to 49 N/mm when inclusion of protein was

increased to 40%. Monti et al. (2016) investigated the influence of fibre inclusion on extruded

dog foods. They reported that kibbes with 12% of guava fibre were characterised by

significantly higher (P<0.001) cutting force (3.4 kg.f) than extrudates with no addition of guava

fibre (2.4 kg.f). Furthermore, the cutting force differed significantly (P<0.001) depending on

the kind of fibre used: 4.1 kg.f for sugarcane fibre and 3.1 kg.f when adding guava fibre. The

level of total dietary fibre equalled 166 g/kg DM in both foods. To evaluate the cutting force

Monti et al. (2016) used texturometer with a Warner-Bratzler Knife probe. The researchers

concluded that in general the lower the inclusion of protein and fibre, the harder the kibbles are

when looking into the same kind of ingredients and providing the same conditions during

extrusion. However, when observing the relationship between the level of macronutrients from

various origin and texture of extrudates (expansion degree, hardness etc.), the outcomes are

inconsistent (Willard, 2003, Monti et al., 2016, Ye et al., 2018). This is due to the specific

physicochemical properties of macronutrients depending on the raw materials used, and the

interactions between them during extrusion. Those mechanisms are shortly described in the

literature review (chapter 2.3., Brennan et al., 2008, Alcázar-Alay et. al., 2015, Ye et al., 2018).

During the production of pet food kibbles, fats can be added before extrusion, as a lubricant,

and after drying as a carrier for palatability enhancers. Adding fat to the mash in the pre-

conditioner reduces share action and lower feed temperature in a barrel during extrusion, which

in turn significantly limits the starch gelatinization and expansion of extrudates (chapter 2.3.,

Lin et al., 1997). In case, fat is applied after extrusion on dry kibbles, it will penetrate the

structure without influencing the expansion ratio giving the kibble its low density and moisture

characteristic (Lin et al., 1998). Above implies, that depending on the production process. It is

29

possible to produce kibbles with high-fat content and different texture characteristics.

Additionally, the diversities in processing conditions such as the amount of water available, the

temperature and screw speed have a great influence on the physical properties of the extrudate

(Ye et al., 2018). In this research, neither the raw ingredients nor the production process, but

only the macronutrient level was considered during food selection which might explain the lack

of relation between the macronutrients level and physical characteristics ok kibbles. Another

shortcoming of this investigation is unknown moisture level in 12 out of 18 foods. A recent

study by Everse (2017) showed that the water content in commercially available dry cat food

range between 4 and 12% with an average of 8%. The assumed 8% for foods where the moisture

was not specified gives uncertainty of ± 4% which could meaningfully affect the outcomes. The

difference in macronutrients levels on DM basis could be up to 7% for starch and crude protein,

4% for crude fat and 1% for crude fibre. Moreover, we did not do our own chemical analysis

of the food samples to validate their nutrient levels. Therefore, results concerning the relation

between macronutrients inclusion and texture as well as eating behaviour might be different

when the exact moisture content is known.

Relation between cat food kibble characteristics and ingestion

Ingestion time was positively correlated with the crude protein level and negatively correlated

with hardness measured with the cat model probe on the Instron. Furthermore, biting rate was

positively correlated with hardness measured with the cat model on the Instron and was

negatively correlated with crude protein levels and this is in line with our expectation. We also

expected that the fibre and fat level will be negatively correlated with biting rate and positively

to the time of ingestion but there was no relation found. In this study, the ingestion speed of dry

cat food varied between 2.9 to 12.6 g/min with an average 5.8 g/min which is higher than the

value reported by Becques et. al. (2014) where the ingestion speed was in a range between 3.4

to 5.3 g/min with an average 4.4 g/min. However, our findings agree with Horwitz et al. (2014),

who recorded ingestion speed values between 2.9 to 12.6 g/min with an average of 5.8 g/min.

The higher average ingestion speed in the current study could be explained by the fact that the

cats were fed 5 g of food every 2 h whereas in the cited studies they were fed at libitum. Horwitz

et al. (2014) observed that the average size of a meal is 6.0 g (2.8 to 17.4 g) and an average

break between meals is 18.09 min (4-34 min) for cats with free access to food. This might

suggest that in our research the cats may have been hungrier and therefore ate faster.

Furthermore, Van Deursen (2017) when studying differences of eating behaviour between

natural cat food sources and commercial diets noted that the chewing rate when consuming dry

cat food was 44.66±3.22 rpm, much higher values were declared by Van Koppen (2017) who

observed 104±4.99 rpm. In our study, the chewing/biting rate values were much lower than in

the previous studies and the mean was 6.78±5.31rpm. This can be explained by the difference

in methodology. Both Van Deursen et. al. (2017) and Van Koppen et al. (2017), when

evaluating chewing rate, counted the up and down movement of cat jaws as a bite. In this study,

a bite/chew was defined as the sound of a cracking kibble between the teeth, because during

eating cat moves the jaws not only when biting, but also when moving a kibble in the mouth

cavity.

The optimal ratio of energy macronutrient composition of cat diet between protein, fat and

carbohydrate is 52%, 36% and 12% respectively (Hewson-Hughes et al., 2011). Commercial

dry cat food contains on average 34.97±3.77 % crude protein, 16.78±4.08 crude fat, 36.99±6.12

starch and 3.67±1.78 crude fibre (Van Deursen et. al., 2017), that gives a ratio of energy

macronutrient composition of 31%, 36%, and 33% respectively. Since cats instinctively strive

to eat and reach the desired level of nutrients (Hewson-Hughes et al., 2011), it could be assumed

30

that foods with desirable protein level are craved more and therefore consumed faster. In a

research by SPF Diana Pet Food (2013), in which foods with higher inclusion of protein

(chicken meal) were more palatable for cats, the researchers were wondering whether the

increased palatability was because of higher level of protein or because the high protein kibbles

were harder or if this occurrence was a resultant of these two factors (Fournier 2013).

Interestingly, we did not find correlations between crude protein content and hardness but

increased ingestion time of foods with higher protein inclusion. However, hardness was

positively related to biting rate and negatively correlated with the time of ingestion measured

by the cat model probe (P<0.001). Bailoni et al. (2005) suggested, that the hardness of kibbles

can be related with plaque formation since harder foods are more abrasive that soft foods and

more capable of removing the teeth plaque. Another interesting finding of our study is that cats

bite significantly more on turbine-shaped kibbles than on the triangle-shaped and disc-shaped.

If hardness and turbine shape are the factors that encourage cats to bite more, then hard turbine-

shaped kibbles should be recommended for cats with oral problems because the more bites the

better plaque removal from teeth and decreased tartar development. Besides, studies in human

eating behaviour proved that multiple chews before swallowing decrease size of the eaten meal,

lowering at the same time energy consumption (Shah et al. 2014, Zhu et al., 2014). The latter

suggests that desired texture and shape of dry cat food could help control speed of ingestion

and intake, but this assumption should be investigated in further research.

Precision of available hardness tests (Kahl, Soltac, Instron) and variability in Instron

texture analysis outcomes when using different probes (platen, blade, cone, cat model)

when evaluating cat food kibbles

Since there is no clear conclusion on the way of texture testing in pet food industry, several

methods suggested by Food Technology Corporation, as well as some technics currently used

in feed and pharmaceutical field in the literature review section (chapter 2.2) are presented. In

this research, when assessing hardness by Kahl (pellet hardness tester used in feed industry)

and Soltac MT50 (tablet hardness tester used in pharmacy) twelve measurements were

performed, from which the highest and the lowest were skipped and the mean of ten repetitions

was calculated. However, for the hardness analysis with Instron seven repetitions were made

for each experimental food. When comparing outcomes of Kahl, Soltac and Instron with platen

probe, Kahl hardeners tester provided the most precise results, what is different from our

expectations. If we had applied the same methodology and omitted the lowest and highest

values from the Instron tests, the CV would change from average 21% in the range from 9% to

32%, to an average 14% in a range from 5% to 23% for platen probe, from average 19% in the

range from to 19% in a range from 15% - 29% for blade probe, from average 0.19 in the range

from 15% to 29% to an average 13% in a range from 3% - 29% for blade probe, from an average

20% in the range from 4% to 38% to an average 12% in a range from 5% to 22% for cone probe

and from an average 27% in the range from 11% to 43% to an average 17% within a range from

10% to 33% for cat model probe (Table 16). The recalculated average and standard deviation

of investigated foods are presented in Appendix IV.

Table 16. Average and range of coefficient of variance [%] in results when using different

probes for evaluation Instron probe

Platen Blade Cone Cat model

Average 21 19 20 27

Range 9-32 15-29 4-38 11-43

Average* 14 13 12 17

Range* 5-23 3-29 5-22 1-33

*skipped the highest and lowest value (average means based on 5 repeated tests per food)

31

Omitting the highest and the lowest score improves the precision of measurements for all used

probes meaningfully but increases the gap between the probes used. Furthermore, there are no

reference values for use when evaluating dry cat food and the accuracy remains unknown. If

we compare the precision of hardness measurements made by Kahl, Soltac and Instron with

platen probe, keeping the methodology constant and skipping the highest and lowest value for

all devices, then the best results would be obtained by platen probe. However, if all data is

included, the Instron texture analyser with cone probe would provide the most precise

outcomes.

7 Conclusion

The primary aim of this project was to find out how the physical and chemical properties of dry

foods translate into the way cats eat these foods. The chemical components did not explain the

variation found in measured hardness values among kibbles irrespective of the method of

measurement. Ingestion time was positively correlated with the crude protein level and

negatively correlated with hardness measured with the cat model probe on the Instron. Cats

were biting significantly more on turbine-shaped kibbles than disc- and triangle-shaped. The

biting rate was positively correlated with hardness measured with the cat model on the Instron

and was negatively correlated with crude protein levels. The secondary aim was, to evaluate

the precision of available texture measurement methodologies. The study showed that the

lowest variability of results provided blade probe and the highest the cat model probe.

8 Recommendations

This study was focused on exploring the associations between the chemical and physical

characteristics of cat food kibbles and ingestion behaviour of cat. Besides, the precision of used

texture assessment methods was evaluated. During the research, some shortcomings of the

chosen methods appeared. Therefore it is suggested to:

1. Perform proximate analysis of investigated foods in order to validate the part of results

concerning the relation between macronutrient inclusion and texture as well as ingestion

behaviour

2. Improve the cat model with an artificial cheek and tongue that will protect the kibbles from

sliding off during the tests

3. Develop a method of comparing the size of differently shaped kibbles

4. Investigate the relation between size and texture parameters of cat food kibbles by

measuring surface area, volume, diameter for every specimen separately before performing

texture profile analysis

32

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36

Appendix I. Total number of texture measurements made with

Instron and reasons for excluding some of them from the research

Table 1. Total number of texture measurements made with Instron with platen probe and

reasons for excluding some of them from the research

*Instron was starting measurements at as soon as the crosshead started moving down, with 75% compression often

even not touching the kibble, this could be happening due to wrong test settings or high sensitivity of the machine,

because even a minimal shake when lowering the probe made the Instron start the measurements before the

compression began; ^ theoretically brittleness in the first pick on the graph, however in many cases there is no pic

or the collapse of the line is very “soft”, or there are several soft collapsions and the graphs were hard to interpret

Instron platen probe

Food total nr of

tests

unsuccessful nr of

tests

test performed incorrectly by

Instron*

impossible to obtain

results^

1 7 0

2 12 5 5

3 7 0

4 18 11 11

5 10 3 3

6 21 14 14

7 7 0

8 7 0

9 8 1 1

10 21 14 14

11 7 0

12 12 5 5

13 9 2 2

14 8 1 1

15 7 0 0

16 30 23 21 2

17 11 4 4

18 7 0

37

Table 2. Total number of texture measurements made with Instron with blade probe (ø 0.03

mm) and reasons for excluding some of them from the research

Instron blade probe

Food total number

of tests

unsuccessful nr

of tests

sliding

kibble

graph is not

closed

impossible to

obtain results^

outstanding

result

1 14 7 2 1 3 1

2 10 3 2 1

3 10 3 3

4 10 3 1 1 1

5 10 3 1 2

6 9 2 1 1

7 14 7 1 2 3 1

8* 29 22 9 3 10

9 8 1 1

10 8 1 1

11 9 2 1 1

12 8 1 1

13 13 6 4 2

14 11 4 3 1

15 11 4 3 1

16 15 8 1 6 1

17 10 3 3

18 9 2 1 1

*small turbine-shaped kibbles for kittens with an uneven surface. The kibbles were often sliding during the test

from underneath the probe; ^ theoretical brittleness in the first pick on the graph, however in many cases there is

no pic or the collapse of the line is very “soft”, or there are several soft collapsions and the graphs were hard to

interpret

Table 3. Total number of texture measurements made with Instron with cone probe (30°) and

reasons for excluding some of them from the research

*small turbine-shaped kibbles for kittens with an uneven surface. The kibbles were often sliding during the test

from underneath the probe; ^ theoretical brittleness in the first pick on the graph, however in many cases there is

no pic or the collapse of the line is very “soft”, or there are several soft collapsions and the graphs were hard to

interpret.

Instron cone probe

Food total number

of tests

unsuccessful nr

of tests

sliding

kibble

graph is not

closed

impossible to

obtain results^

outstanding

result

1 10 3 2 1

2 9 2 1 1

3 9 2 2

4 9 2 2

5 10 3 3

6 10 3 2 1

7 12 5 3 2

8* 27 20 13 2 3 1

9 11 4 1 3

10 12 5 1 4

11 11 4 4

12 12 5 5

13 12 5 1 4

14 13 6 6

15 14 7 4 3

16 12 5 4 1

17 12 5 3 2

18 10 3 3

38

Table 4. Total number of texture measurements made with Instron with cat model and reasons

for excluding some of them from the research Instron cat model probe

Food total number

of tests

unsuccessful nr

of tests

sliding

kibble

graph is not

closed

impossible to

obtain results^

outstanding

result

1 11 4 3 1

2 15 8 5 3 1

3 8 1 1

4 8 1 1

5 15 8 4 4

6 18 11 7 4

7 7 0

8* 20 13 8 5

9 10 3 3

10 8 1 1

11 18 11 7 4

12 9 2 1 1

13 10 3 1 2

14 14 7 4 2 1

15 11 4 3 1

16 8 1 1

17 10 3 3

18 11 4 2 2 1

*small turbine-shaped kibbles for kittens with an uneven surface. The kibbles were often sliding during the test

from underneath the probe; ^ theoretical brittleness in the first pick on the graph, however in many cases there is

no pic or the collapse of the line is very “soft”, or there are several soft collapsions and the graphs were hard to

interpret

39

Appendix II. Correction formula for cat model probe

S1 = 17 cm

S2 = 13 cm

cos 40° = 0.77

cos 55° = 5.75

cos 40° / cos 55° = 1.35

S1 / S2 = 1.31

F2 = 1.31*1.35 * F1 =1.77 * F1

40

Appendix III. Detailed intake protocol 17.07.2018 - 27.07.2018

Study: Kibble chemical and texture characteristics on feeding behaviour in cats

Student: Agata Kozuchowicz

1. Materials: - experimental foods (stored in the grey cabinet in the kitchen),

- experimental meals for the whole day (already prepared in the cabinet in the

metabolism room),

- 2 x go pro cameras,

- scale,

- report 1 sheet for today,

- clean and dry bowls,

- cutting board A and cutting board B,

- 2 pens

- wrapping foil

- trays

2. Morning feeding: 2.1 8.00 h Cats are fed separately in the home-cages 20% of their daily intake with dry food

2.2 Morning meals for experimental cats are already prepared. They are stored in the cabinet in the

metabolism room (cabinet behind the door). Bowls are placed on the trays (according to the cat

names written on the trays)

2.3 Place the bowls with food in the individual feeding cages following the names on the trey

2.4 Prepare wet food meals (200g) for the 2 cats (Lord and Kasko) that are housed together with

the experimental cats.

- put the bowl on the scale

- press TARE

- fill the bowl with 200g of wet food

- put the bowl on the table and chopped the food for small pieces with a fork

- put the bowl to the feeding cage

- repeat for the second cat

2.5 Let the cats into the cages and lock them in (repeat this procedure for each group separately)

2.6 When cats are eating, there is a time to clean their rooms (following indications in the cleaning

and disinfection protocol)

2.7 When the cleaning is done (and the kennel is dry) let the cats move to their rooms (each group

separately)

2.8 Note the intake in the intake protocol (MAP folder), remove the bowls and put them in the

dishwasher

2.9 Clean the feeding cages (vacuum hairs and if necessary wash with a wet cloth)

41

3. Feeding procedure during the adaptation and testing day: 3.1 There are 4 feeding rounds for every cat

3.2 There are two cats tested at the same time (one male and one female).

3.3 Cats are placed in the experimental feeding cages separately for every test.

3.4 Male cats (1,3,5,7) are always tested in the cage A. Female cats (2,4,6,8) are always tested in

the cage B (Table 1)

3.5 Feeding cats with experimental foods starts at 10.00h (round 1) and finishes at 16.55h (the end

of round 4)

3.6 During feeding cats with the experimental foods keep the area quiet and calm.

Table 1. Cat feeding plan with experimental foods during adaptation and test days &

16,17,19,20,23,24,26 July 2018, with an indication of placing cats in the individual feeding

cages.

round

1

cat (nr) in

feeding cage

(A or B)

round

2

cat (nr) in

feeding cage

(A or B)

round

3

cat (nr) in

feeding cage

(A or B)

round

4

cat (nr) in

feeding cage

(A or B)

A B A B A B A B

10.00 h 1 2 12.00 h 1 2 14.00 h 1 2 16.00 h 1 2

10.15 h 3 4 12.15 h 3 4 14.15 h 3 4 16.15 h 3 4

10.30 h 5 6 12.30 h 5 6 14.30 h 5 6 16.30 h 5 6

10.45 h 6 8 12.45 h 6 8 14.45 h 6 8 16.45 h 6 8

4. Preparation for adaptation and testing intake: After the morning feeding and cleaning procedures are done (no later than 9.30 h):

4.1 Ensure the cameras are working properly, are charged and it is enough storage space for

recordings (the cameras are kept on the bottom shelve in the grey cabinet in the kitchen)

4.2 Take the foods that are going to be tested during the coming round (already prepared on the

treys on the bottom shelves in the cabinet in the metabolism room) and put them on the table in

the metabolism room.

4.3 Place the scale, report 1 sheet for today, 2 pens on the table next to the experimental foods.

4.4 Check the individual feeding cages. They should be clean and dry. Mount the camera A to cage

A, and camera B to cage B like in the Figure 1a

4.5 Make sure that both cameras work properly (press the button on the right top (recording button),

the camera should shortly beep 3 times and the recording should start when the red spot will

show up on the screen, Figure 1b). To stop the recording press the recording button, the camera

should beep 3 times and the recording will be saved.

4.6 During the adaptation and testing days, there are 4 rounds for each cat (Attachment 1) Every

cat has an assigned number. The cats’ names are written on their collars. The assigned numbers

are in Attachment 1

42

Figure 1. a: Feeding cage with the correctly placed cutting board and camera; b: recording

button on the right top of the camera

5. Procedure for the test round: 5.1Place the cutting board A into cage A and the cutting board B into cage B, as indicated in

the picture (Figure 1a)

5.2 Put the food for the male cat on the cutting board A in the experimental cage A and for the

female cat on the cutting board B in the experimental cage B

5.3 Take male cat (1,3,5 or 7) from the room and place it in the waiting cage following the

order in Table 1. Close the cage

5.4 Take the female cat from the room. Start the cameras. After 3 short beeps from both cameras

place the female cat in the experimental cage B and close the cage

5.5 Bring the male cat from the waiting cage to the experimental cage A and close the

cage (Table 1) and quietly move behind the feeding cages where the cats can’t see you and stay

silent till the time you do not hear any cracking kibbles (ca. 1 minute). Check carefully if there

are no kibbles on the cutting boards. When the cats are finished, or after 10 minutes open the

cages and press the recording button to switch off the cameras (you should hear 3 beeps)

5.6 Take the cats back to their groups

5.7 Weight the remaining food and write the amount it the REPORT 1

5.8 Wash the cutting boards with hot water in the kitchen and dry with a towel

5.9 Clean the experimental cages if necessary (vacuum hairs and if necessary wash with

wet cloth)

5.10 Follow this routine starting from point 4.1 for the next 3 rounds. New round starts

every 15 minutes (e.g. 10.00 h, 10.15 h, 10.30 h, 10,45 h etc., Table 1)

6. Transferring obtained recordings from the camera to the computer

and creating a backup copy: 6.1 Transfer all recording to the computer (MEDION) in the kitchen (Folder EATING

BEHAVIOUR KIBBLES\recordings) on the pulpit and make a backup copy:

6.2 on the external disc (I:\EATING BEHAVIOUR KIBBLES\recordings). It is kept in the MAP

folder.

6.3 After each round check the battery level and storage space of the cameras and if the battery is

less than a half, plug the cameras to the power. If there is not sufficient storage space on the

device, delete the recordings that are already transferred to the computer and stored in the

backup copy.

a b

43

7. Preparing morning meal 7.1 During the break between round 1 and 2 prepare the

morning meal for the next day

7.2 Put the bowl on the scale

7.3 Press TARE

7.4 Weight the morning meal of the food (Table 2)

7.5 Secure the bowl with plastic foil

7.6 Put the ready food on the tray (following the names on

the tray)

7.7 Follow this steps (from p. 8.1) to prepare morning

meals for the 8 cats assigned to the experiment.

7.8 Put the treys with foods to the cabinet in the metabolic

room (behind the door)

8. Preparing experimental meals 8.1 During the break between round 2 and 4 prepare the morning meal for the next day

8.2 Put the bowl on the scale

8.3 Press TARE

8.4 Weight 5g of the food (Make sure there are no

broken kibbles or differently shaped kibbles in

the bowl) and write the exact amount in the

Report 1

8.5 Wrap the bowl with a protective foil and place

on the tray following the numbers of a cat for

whom the food is prepared and the number of

round (Attachment 2, Figure 2)

8.6 Follow the same steps (starting from point 8.2)

till all experimental meals for the next day are

prepared

8.7 Store the experimental food on the two bottom shelves in the cabinet in the metabolic room

9. Calculating the amount of afternoon meal.

When the 3rd round is finished calculating the afternoon intake for every cat separately (the rest

of daily intake corrected for the intake during the test (Attachment 2) and leftovers Report 1,

(the energy value [kcal] for all experimental foods are included in the Attachment 3) and prepare

the afternoon meals:

9.1 Put the bowl on the scale

9.2 Add leftovers from the morning feeding

9.3 Press TARE

9.4 Weight the proper amount of the food calculated in Report 1

9.5 Put the bowl on the tray following the names on it

9.6 Prepare meals for all 8 cats starting from the point 6.1 and for the 2 cats housed together with

them (point 1.4)

Table 2. Morning meal during

adaptation and tasting days (20% of

daily intake)

Figure 2. Experimental meals wrapped

with protective foil and placed on the tray

Catmorning meal [g] (20%

of daily intake)

Aal 7.6

Anouk 9.6

Bella 8.8

Jill 9.2

Bas 12

Kasko 12

Siske 16.4

Lord 9.6

44

9.7 In case there are leftovers of experimental food during round 4, correct the afternoon meal one

more time.

10. Afternoon feeding 10.1 The afternoon feeding starts at 17.00 h

10.2 Put the bowls with a meal for every cat separately in their regular individual feeding cages.

10.3 Let the cats into the cages and lock them in (repeat this procedure for each group separately)

10.4 When cats are done with eating, let them move into their room (each group separately)

10.5 Note the intake in the intake protocol (MAP folder), remove the bowls and put them in the

dishwasher

10.6 Clean the feeding cages (vacuum hairs and if necessary wash with a wet cloth)

11. Before leaving 11.1 Transfer all recording to the computer in the kitchen (Folder EATING BEHAVIOUR

KIBBLES\recordings) on the pulpit and make a backup copy: on the black flash drive (STORE

N GO:\EATING BEHAVIOUR KIBBLES\recordings) and on the blue flash drive

(Cnmemory:\EATING BEHAVIOUR KIBBLES\recordings). They are stored in the MAP

folder.

11.2 Take a picture of the REPORT 1 from this day and transfer it to the computer in the kitchen

and make two backup copies (Folder EATING BEHAVIOUR KIBBLES\Report 1; external

disc (I:\EATING BEHAVIOUR KIBBLES\Report 1)

11.3 Place all the documents and the two external discs in the MAP Folder and inform the co-

workers (WhatsApp group) if there are any unusual observation concerning cats or the facility.

11.4 Tidy up the kitchen and the metabolism room. Clean the feeding cages with hot water and

detergent if necessary. Put the bowls and cutting boards in the dishwasher. Start the dishwasher.

Turn off the light when leaving.

45

Attachment 1. Experiment plan

Cats 1: Kasko, 2:Aal, 3: Siske, 4: Anouk, 5: Lord, 6: Jill, 7: Bas, 8: Bella

Cats: 1: Kasko, 2: Aal, 3: Siske, 4: Anouk, 5: Lord, 6: Jill, 7: Bas, 8: Bella

2018MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY SUNDAY

09 10 11 12 13 14 15Diet switch day I

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

75% wet food + 25% dry food

Diet switch day II

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

50% wet food + 50% dry food

Diet switch day III

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

25% wet food + 75% dry food

Diet switch day IV

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

100% dry food

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

16 17 18 19 20 21 22Adaptation day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Test day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

Adaptation day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Test day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

July

46

2018MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY SUNDAY

23 24 25 26 27 28 29Adaptation day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Test day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

Test day

8.00h Morning feeding (20%)

17.00h Evening feeding (rest of

the daily portion corrected for

intake during tests)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

Rest day

8.00h Morning feeding (50%)

16.00h Evening feeding (50%)

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

I: test feeding (5g)

10.00h, cats 1 & 2

10.15h, cats 3 & 4

10.30h, cats 5 & 6

10.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

II: test feeding (5g)

12.00h, cats 1 & 2

12.15h, cats 3 & 4

12.30h, cats 5 & 6

12.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

III: test feeding (5g)

14.00h, cats 1 & 2

14.15h, cats 3 & 4

14.30h, cats 5 & 6

14.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

IV: test feeding (5g)

16.00h, cats 1 & 2

16.15h, cats 3 & 4

16.30h, cats 5 & 6

16.45h, cats 7 & 8

July

47

Attachment 2. . Experimental diets set up

day date day round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8

I

Monday

AD

AP

TA

TIO

N

16.0

7

1 12 4 9 3 2 12 1 11

2 5 14 11 16 9 11 18 4

3 3 1 18 12 13 16 5 14

4 1 9 16 14 18 2 13 3

kcal sum 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

Tues

day

TE

ST

17.0

7

1 3 1 16 12 13 11 5 14

2 5 14 18 16 9 12 13 3

3 1 9 11 3 2 16 18 4

4 12 4 9 14 18 2 1 11

kcal sum 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

II

Thurs

day

AD

AP

TA

TIO

N

19.0

7

1 14 3 13 9 14 18 9 5

2 16 5 2 1 12 4 14 13

3 2 16 4 2 4 5 3 12

4 18 11 12 13 11 1 16 1

kcal sum 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

Fri

day

TE

ST

20.0

7

1 16 5 2 1 11 4 3 12

2 14 3 13 9 4 18 16 1

3 18 11 12 13 14 1 9 5

4 2 16 4 2 12 5 14 13

kcal sum 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

48

day date

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8

III

Monday

AD

AP

TA

TIO

N

23.0

7

1 13 12 14 18 5 14 4 18

2 9 2 3 11 1 3 2 16

3 4 13 5 4 3 13 12 9

4 11 18 1 5 16 9 11 2

kcal

sum 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

Tues

day

TE

ST

24.0

7

1 4 18 5 4 16 3 2 9

2 11 2 1 5 3 13 12 16

3 13 12 14 18 5 9 11 2

4 9 13 3 11 1 14 4 18

kcal

sum 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

IV

Thurs

day

TE

ST

26.0

7

1

2

3

4

kcal

sum

49

Attachment 3. List of experimental diets and their energy content Diet

Number in research kcal in 5g [as it is]

Animonda Integra Protect Adult Diabetes 1A 22.84

Purina Cat Chow Kitten Kip Kattenvoer 2A 20.46

Animonda Integra Protect Adult Obesitas 3 AD 19.38

Happy Cat Nierdieet 4 BC 23.08

Josera Marinesse 5B 21.51

Royal Canin Sphynx Adult 9 C 23.20

Josera Léger 11 D 19.46

Hill's Feline Indoor Cat Adult Kip 12 DE 18.92

Iams® Cat Mature Hairball Control with Whitefish 13E 20.79

Royal Canin Light Weight Care 14 AE 19.35

Hills science plan healthy ageing 16 AF 23.26

Almo Nature Orange Label Adult Sardientjes 18 F 20.97

Experimental diets – shapes defined by colours:

O ‘disc’ shaped kibbles – orange

Y ‘turbine’ shaped kibbles – blue

Δ ‘triangle’ shaped kibbles - green

Estimation of nutrient content in experimental diets:

A high protein </= 40%

B low protein </= 32.5%

C high fat </= 20%

D low fat </= 10%

E high fiber </= 5.5%

F low fiber </= 2%

O 1,4,13,16

Y 2,5,11,14

Δ 3,9,12,18

50

Report 1.

Mo

nd

ay A

DA

PT

AT

ION

16

.07

.18

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 12 4 9 3 2 12 1 11

weight

[g] 5.13 5.22 4.99 5.28 5.04 5.15 5.07 5.11

2

diet 5 14 11 16 9 11 18 4

cat 8. 5 g

leftovers

weight

[g] 5.29 5.11 5.18 4.98 5.26 5.03 5.20 5.21

3

diet 3 1 18 12 13 16 5 14

cat 5 ate one

kibble before

recording started

weight

[g] 5.18 5.03 5.17 5.13 5.09 5.06 5.15 5.13

4

diet 1 9 16 14 18 2 13 3

cat 8. 5 g

leftovers

weight

[g] 5.04 5.30 5.08 5.10 5.50 5.10 5.02 5.36

leftovers [g] 10.00

leftovers

[kcal] 42.46

experiment

[kcal] 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

119.06 39.28 188.79 80.46 75.95 72.55 115.60 109.11

80 % intake -

exp. meals [g] 28.33 9.35 44.93 19.15 18.07 17.26 27.51 25.97

51

T

ues

day

TE

ST

17

.07.1

8

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 3 1 16 12 13 11 5 14

weight

[g] 5.03 5.05 5.13 5.16 5.11 5.12 5.22 5.00

2

diet 5 14 18 16 9 12 13 3

cat 8. 5 g leftovers

weight

[g] 5.29 5.00 5.04 5.09 5.23 5.00 5.01 5.19

3

diet 1 9 11 3 2 16 18 4

cat 8. 5 g leftovers;

cat 5 ate 1 kibble

before recording

started (probably) weight

[g] 5.07 5.08 5.21 5.08 5.04 5.08 5.24 5.00

4

diet 12 4 9 14 18 2 1 11

cat 5. 1.56g

leftovers (6

kibbles); cat 4 ate 2

kibbles after

recording was

stopped

weight

[g] 5.12 5.06 5.13 5.08 5.03 5.03 5.01 5.04

leftovers [g] 1.56 10.00

leftovers

[kcal] 7.2 42.46

experiment

[kcal] 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

119.06 39.28 188.79 80.46 83.15 72.55 115.60 109.11

80 % intake -

exp. meals [g] 28.33 9.35 44.93 19.15 19.79 17.26 27.51 25.97

52

T

hu

rsd

ay A

DA

PT

AT

ION

19

.07

.18

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 14 3 13 9 14 18 9 5

cat 6. left one

kibble; cat 8. 5g

leftovers

weight

[g] 5.08 5.07 5.11 5.16 5.03 5.16 5.27 5.04

2

diet 16 5 2 1 12 4 14 13

cat 6. leftovers

4.79; cat 8 0.63

g (3 kibbles

leftovers) weight

[g] 5.12 5.18 5.06 5.00 5.15 5.05 5.02 5.18

3

diet 2 16 4 2 4 5 3 12

cat 8. 5g

leftovers

weight

[g] 5.04 5.00 5.09 5.04 5.08 5.11 5.15 5.02

4

diet 18 11 12 13 11 1 16 1

cat 8. 5g

leftovers

weight

[g] 5.16 5.15 5.09 5.09 5.11 5.02 5.05 5.09

leftovers [g] 4.79 16.00

leftovers

[kcal]

22

64.00

experiment

[kcal] 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

117.67 44.15 192.42 74.08 80.56 88.24 116.53 127.86

80 % intake -

exp. meals [g] 28.00 10.51 45.79 17.63 19.17 21.00 27.73 30.43

53

Fri

day

TE

ST

20

.07

.18

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 16 5 2 1 11 4 3 12

cat 6. 5.01 g

leftovers

weight

[g] 5.15 5.18 5.03 5.07 5.50 5.10 5.12 5.06

2

diet 14 3 13 9 4 18 16 1

cat 5. 0.65 g (3

kibbles)

leftovers;

cat 8 4.91 g

leftovers weight

[g] 5.02 5.10 5.14 5.01 5.13 5.17 5.00 5.16

3

diet 18 11 12 13 14 1 9 5

cat 8 5.25g

leftovers

weight

[g] 5.23 5.13 5.08 5.06 5.08 5.11 5.06 5.25

4

diet 2 16 4 2 12 5 14 13

cat 8 1.92g

leftovers

weight

[g] 5.08 5.01 5.06 5.00 5.00 5.05 5.00 5.00

leftovers [g] 0.65 5.01 12.08

leftovers

[kcal] 23.08 52.35

experiment

[kcal] 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

117.67 44.15 192.42 74.08 80.56 89.32 116.53 116.21

80 % intake -

exp. meals [g] 28.00 10.51 45.79 17.63 19.17 21.26 27.73 27.65

54

Mo

nd

ay A

DA

PT

AT

ION

23

.07

.18

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 13 12 14 18 5 14 4 18

weight

[g] 5.04 5.02 5.03 5.14 5.08 5.09 5.16 5.09

2

diet 9 2 3 11 1 3 2 16

noise outside

(drying during

the first 2 cats)

weight

[g] 5.18 5.10 5.15 5.20 5.01 5.22 5.06 5.02

3

diet 4 13 5 4 3 13 12 9

cat 4. 3.58g; cat

8 0.66g left (2

kibbles)

weight

[g] 5.08 5.13 5.13 5.02 5.21 5.05 5.09 5.29

4

diet 11 18 1 5 16 9 11 2

weight

[g] 5.01 5.03 5.02 5.09 5.00 5.10 5.05 5.01

leftovers [g] 3.58 0.66

leftovers [kcal] 17.00 3.00

experiment

[kcal] 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

115.19 46.61 192.59 93.35 74.38 71.93 119.79 63.04

80 % intake -

exp. meals [g] 27.41 11.09 45.83 22.21 17.70 17.12 28.51 15.00

55

Tu

esd

ay T

ES

T 2

4.0

7.1

8

day

round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 4 18 5 4 16 3 2 9 cat 4 refusals; cat

8 refusals (ate

after, too big or

too hard kibbles,

pain during

biting them??, )

weight

[g] 5.13 5.22 5.14 5.02 5.12 5.18 5.06 5.33

2

diet 11 2 1 5 3 13 12 16

weight

[g] 5.16 5.09 5.20 5.17 5.11 5.11 5.12 5.05

3

diet 13 12 14 18 5 9 11 2

weight

[g] 5.13 5.07 5.03 5.03 5.04 5.03 5.08 5.08

4

diet 9 13 3 11 1 14 4 18 cat 5 0.48 g

leftovers (3

kibbles); cat 8

0.29 g leftovers

(1 kibble) weight

[g] 5.18 5.11 5.18 5.10 5.00 5.06 5.25 5.09

leftovers [g] 5.02 0.48 0.29

leftovers

[kcal] 23.08 3.00 2.00

experiment

[kcal] 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

80 % intake

[kcal] 201.71 127.75 275.67 161.37 161.37 154.64 201.71 147.92

80 % intake -

exp. meals

[kcal]

115.19 46.61 192.59 99.43 77.38 71.93 119.79 62.04

80 % intake -

exp. meals [g] 27.41 11.09 45.83 23.66 18.41 17.12 28.51 14.76

56

Th

urs

day

TE

ST

26

.07

.18

day round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8 notes

1

diet 4 4 16 3

cats 4, 6, 8

refusal

weight [g] 5.15 5.07 5.15 5.22

2

diet 2 5

cat 8 refusal

weight [g] 5.01 5.07

3

diet 11 1

cat 8 refusal

weight [g] 5.27 5.17

4

diet 4 9

cat 8 refusal

weight [g] 5.12 5.14

leftovers [g] 5.15 5.07 20

leftovers [kcal] 23.08 23.08 86.93

experiment [kcal] 23.08 23.08 86.26 86.93

80 % intake [kcal] 161.37 154.64 201.71 147.92

80 % intake - exp. meals

[kcal] 161.37 154.64 115.45 147.92

80 % intake - exp. meals

[g] 38.40 36.80 27.47 35.20

57

The content of energy in experimental meals:

day day round cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8

Monday 16.07.18

1 18.92 23.08 23.20 19.38 20.46 18.92 22.84 19.46

2 21.51 19.35 19.46 23.26 23.20 19.46 20.97 23.08

3 19.38 22.84 20.97 18.92 20.79 23.26 21.51 19.35

4 22.84 23.20 23.26 19.35 20.97 20.46 20.79 19.38

kcal sum 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

Tuesday 17.07.18

1 19.38 22.84 23.26 18.92 20.79 19.46 21.51 19.35

2 21.51 19.35 20.97 23.26 23.20 18.92 20.79 19.38

3 22.84 23.20 19.46 19.38 20.46 23.26 20.97 23.08

4 18.92 23.08 23.20 19.35 20.97 20.46 22.84 19.46

kcal sum 82.65 88.47 86.88 80.91 85.41 82.09 86.11 81.27

Thursday 19.07.18

1 19.35 19.38 20.79 23.20 19.35 20.97 23.20 21.51

2 23.26 21.51 20.46 22.84 18.92 23.08 19.35 20.79

3 20.46 23.26 23.08 20.46 23.08 21.51 19.38 18.92

4 20.97 19.46 18.92 20.79 19.46 22.84 23.26 22.84

kcal sum 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

Friday 20.07.18

1 23.26 21.51 20.46 22.84 19.46 23.08 19.38 18.92

2 19.35 19.38 20.79 23.20 23.08 20.97 23.26 22.84

3 20.97 19.46 18.92 20.79 19.35 22.84 23.20 21.51

4 20.46 23.26 23.08 20.46 18.92 21.51 19.35 20.79

kcal sum 84.04 83.60 83.25 87.28 80.81 88.40 85.18 84.06

Monday 23.07.18

1 20.79 18.92 19.35 20.97 21.51 19.35 23.08 20.97

2 23.20 20.46 19.38 19.46 22.84 19.38 20.46 23.26

3 23.08 20.79 21.51 23.08 19.38 20.79 18.92 23.20

4 19.46 20.97 22.84 21.51 23.26 23.20 19.46 20.46

kcal sum 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

Tuesday 24.07.18

1 23.08 20.97 21.51 23.08 23.26 19.38 20.46 23.20

2 19.46 20.46 22.84 21.51 19.38 20.79 18.92 23.26

3 20.79 18.92 19.35 20.97 21.51 23.20 19.46 20.46

4 23.20 20.79 19.38 19.46 22.84 19.35 23.08 20.97

kcal sum 86.53 81.14 83.08 85.02 86.99 82.71 81.92 87.88

58

Appendix IV. Hardness mean ± SD, and CV, its average and range

of investigated kibbles when using different probes for evaluation

and skipped the highest and lowest value (average means based on

5 repeated tests per food)

Instron probe

Food Platen Blade Cone Cat model

Mean±SD CV [%] Mean±SD CV [%] Mean±SD CV [%] Mean±SD CV [%]

1 14.29±2.31 16 3.59±0.44 12 6.01±0.27 5 3.57±0.63 18

2 12.78±1.37 11 2.84±0.23 8 3.61±0.46 13 1.73±0.32 18

3 69.56±8.59 12 5.35±0.18 3 3.73±0.53 14 5.53±0.55 1

4 18.67±4.22 23 1.91±0.15 8 3.65±0.55 15 2.07±0.47 23

5 11.99±1.58 13 3.77±0.59 16 5.10±0.52 1 2.31±0.63 27

6 13.31±1.57 12 3.59±0.34 9 5.28±0.81 15 3.49±0.87 25

7 18.44±3.44 19 18.33±3.40 19 4.62±0.53 12 4.49±0.68 15

8 8.21±1.44 18 1.84±0.21 11 2.86±0.57 20 1.42±0.32 22

9 23.36±3.50 15 4.42±0.54 12 6.65±0.46 7 4.47±1.20 27

10 15.55±1.29 8 2.95±0.22 8 6.22±0.52 8 3.71±0.20 5

11 23.97±3.68 15 3.9±0.52 13 6.53±0.51 8 3.36±0.53 16

12 23.55±5.15 22 3.28±0.31 10 5.38±0.51 9 2.59±0.13 5

13 36.43±1.91 5 3.48±0.62 18 4.52±0.99 22 3.18±0.28 9

14 12.22±0.69 6 2.97±0.41 14 5.56±0.45 8 2.56±0.22 9

15 8.32±0.91 11 1.85±0.53 29 3.15±0.42 13 2.00±0.65 33

16 13.23±1.59 12 2.76±0.33 12 3.39±0.17 5 2.61±0.45 17

17 15.15±2.67 18 2.93±0.44 15 4.14±0.71 17 1.79±0.37 21

18 14.43±1.96 14 4.02±0.64 16 6.45±0.94 15 2.88±0.44 15

Average 14 13 12 17

Range 5-23 3-29 5-22 1-33

59

Appendix V. Ingredients of experimental foods

Food Ingredients

1.Animonda Integra

Protect Adult Diabetes

greaves meal, potatoes (dried), peas (mixed), pea protein, poultry fat, beef suet,

salmon oil, poultry liver, cellulose, calcium carbonate, sodium chloride, green-

lipped muscle powder

2. Purina Cat Chow

Kitten Chicken

meat and animal products (min. 4% of chicken), cereals, vegetables, vegetable

poultry extracts (min. 2% of soya), oils and fats, fish and fish products (min. 2%

of salmon), minerals, yeast

3. Animonda Integra

Protect Adult Obesity

poultry meal (low ash), potatoes (dried), pea protein, beet pulp, cellulose, poultry

meal, poultry liver, salmon oil, yeast, green lipped mussel powder, hydrolysed

cartilage

4. Happy Cat Kidney

rice flour, potato flakes, poultry fat, poultry protein, greaves, potato protein,

cellulose, fish meal, haemoglobin, sugar beet molasses (sugar), meat meal, apple

pomace (0.4%), sodium chloride, linseed (0.2%), yeast, potassium chloride,

seaweed (0.06%), yucca schidigera (0.04%), chicory root (0.04%), yeast

(extracted), milk thistle, artichoke, dandelion, ginger, birch leaves, nettle,

camomile, coriander, rosemary, sage, licorice root, thyme (dried herbs total:

0.05%) dried hydrolysed proportionately

5. Josera Marinesse dried salmon, rice, dried potato, poultry fat, sugar beet pulp, potato protein,

hydrolysed fish protein, minerals

6. Royal Canin Indoor 27

corn, poultry protein (dried), rice, vegetable protein isolate, wheat, animal fat,

animal protein (hydrolysed), lignocellulose, minerals, beet pulp, soya oil, fructo-

oligosaccharides, yeast, fish oil

7. Hill's Feline Optimal

Care Adult Chicken

poultry meat meal, wheat, animal fats, maize, maize gluten, rice, digest, minerals,

beet pulp, fish oil

8. Smølke kitten

chicken meal (25%), corn gluten, corn, chicken fat (stabilized with natural

tocopherols), rice, sorghum, beet pulp, lamb flour (4%), fish meal (2%), vitamins

and minerals mix, hydrolysed protein, cellulose ( 1.3%), yeast (1%), fish oil

(0.8%) , chicory (0.7%)

9. Royal Canin Sphynx

Adult

poultry protein (dried), animal fat, rice, vegetable protein isolate, maize, vegetable

fibres, pork protein (dried), animal protein (hydrolysed), wheat, corn gluten feed,

beet pulp, minerals, yeasts, fish oil, tomato (source of lycopene), soya oil, fructo-

oligosaccharides, yeast hydrolysate (source of mannan-oligosaccharides), borage

oil, marigold extract (source of lutein)

60

Food Ingredients

10. Felix Indoor

Sensations

grain (38%), meat and animal by-products (10%), plant protein extracts, oils and

fats, vegetable by-products (green and orange kibble: 0.15% dried parsley is

equivalent to 1% parsley), vegetables (2% dried chicory roots), minerals, yeast

11. Josera Léger

poultry meat meal, maize, greaves, rice, cellulose, beet pulp, poultry protein

(hydrolysed), corn protein, chicken fat, chicken liver, dried, potassium chloride,

monosodium phosphate

12. Hill's Feline Indoor

Cat Adult Chicken

poultry meat meal (min. chicken 40%), maize, rice, corn gluten meal, cellulose,

digest, animal fat, vegetable oil, potassium chloride, calcium sulphate, sodium

chloride

13. Iams Cat Mature

Hairball Control with

Whitefish

chicken, chicken by-product meal, ground whole grain corn, corn grits, corn gluten

meal, dried beet pulp, salmon, powdered cellulose, natural flavour, dried egg

product, caramel colour, potassium chloride, brewers dried yeast, choline chloride,

calcium carbonate, fructooligosaccharides,

14. Royal Canin Light

Weight Care

poultry meal, corn, vegetable protein, vegetable fibres, maize gluten, animal

protein (hydrolysed), animal fat, beet pulp, yeasts, minerals, fish oil, psyllium

(psyllium and covers) (0.5%), soybean oil

15. Albert Heijn Premium

Menu Indoor

meat and animal by-products (17% fresh turkey), cereals, vegetable by-products

(4% cellulose), oils and fats, minerals, yeasts

16. Hills Feline Senior

Healthy Ageing 11+

poultry meat meal (chicken 31%, total poultry content 48%), maize, maize gluten

meal, rice, animal fat, cereals, minerals, meat and animal by-products, vegetable

by-products, oils and fats

17. Royal Canin Sensible

33

poultry protein (dried), animal fat, rice, maize, vegetable protein isolate, maize

gluten, animal protein (hydrolysed), wheat, minerals, beet pulp, yeast, fish oil,

vegetable fibres, soya oil, fructooligosaccharides

18. Almo Nature Orange

Label Adult Sardine

fish and meat by-products (45%, incl. 10% sardines and 27% fresh meat), grain,

oils and fats, vegetable protein extract, yeast, minerals, vegetable by-products

61

Appendix VI. Additional data

Table 1. Surface area, thickness and kibbles weight of investigated foods.

Food Surface area [cm2] ± SD Thickness [mm] ± SD Weight of 100 kibbles [g]

1 3.64 ± 0.69 4.88 ± 0.75 14.80

2 2.54 ± 0.37 4.12 ± 0.44 11.95

3 2.79 ± 0.17 4.56 ± 0.39 27.45

4 5.16 ± 0.52 5.55 ± 0.57 25.95

5 4.47 ± 0.60 5.52 ± 0.56 27.30

6 3.34 ± 0.33 6.07 ± 0.37 22.65

7 4.41 ± 0.27 4.78 ± 0.25 27.90

8 2.90 ± 0.33 5.42 ± 0.24 9.15

9 3.77 ± 0.25 6.39 ± 0.30 32.70

10 6.59 ± 1.48 4.85 ± 0.24 20.50

11 4.28 ± 0.66 5.91 ± 0.50 25.35

12 3.03 ± 0.28 5.59 ± 0.52 21.55

13 8.03 ± 0.39 4.45 ± 0.30 21.05

14 3.41 ± 0.35 4.72 ± 0.29 14.25

15 2.75 ± 0.43 6.49 ± 0.75 18.00

16 6.21 ± 0.90 3.96 ± 0.25 15.95

17 3.63 ± 0.34 4.00 ± 0.34 18.20

18 2.46 ± 0.28 5.03 ± 0.51 26.45

Table 2. Hardness

Food Kahl [kg] ±

SD

Sotax [kg] ±

SD

I platen [kg] ±

SD

I cone [kg] ±

SD

I blade [kg] ±

SD

I cat [kg] ±

SD

1 12.83 ± 2.69 5.88 ± 1.48 14.73 ± 3.79 3.38 ± 0.99 5.98 ± 0.89 3.38 ± 1.49

2 10.25 ± 1.31 3.51 ± 1.12 12.73 ± 1.74 2.84 ± 0.29 3.59 ± 0.65 2.84 ± 0.38

3 4.29 ± 0.52 4.23 ± 0.65 68.60 ± 12.32 5.37 ± 0.24 4.05 ± 1.16 5.37 ± 0.77

4 8.31 ± 1.68 4.25 ± 0.45 19.07 ± 6.18 1.91 ± 0.21 3.67 ± 0.64 1.91 ± 0.54

5 8.42 ± 2.34 5.15 ± 1.42 11.79 ± 3.07 3.71 ± 0.97 5.21 ± 0.84 3.71 ± 0.82

6 11.63 ± 1.75 6.41 ± 0.70 13.16 ± 2.13 3.56 ± 0.55 5.23 ± 1.04 3.56 ± 1.05

7 14.23 ± 2.24 5.75 ± 1.39 17.99 ± 4.44 17.91 ± 4.41 4.64 ± 0.74 17.91 ± 0.75

8 4.44 ± 0.35 2.61 ± 0.40 8.22 ± 1.94 1.85 ± 0.37 3.03 ± 0.94 1.85 ± 0.53

9 16.4 ± 1.47 8.66 ± 0.79 24.12 ± 6.18 4.44 ± 0.78 6.74 ± 0.77 4.44 ± 1.94

10 12.42 ± 1.12 6.38 ± 0.76 15.48 ± 1.94 2.90 ± 0.36 6.17 ± 0.84 2.90 ± 0.54

11 15.9 ± 2.13 7.07 ± 0.88 22.95 ± 5.51 3.83 ± 0.60 6.54 ± 0.95 3.83 ± 0.54

12 8.44 ± 1.06 6.82 ± 0.66 23.39 ± 7.42 3.29 ± 0.39 5.28 ± 1.03 3.29 ± 0.30

13 13.69 ± 1.38 6.23 ± 1.40 36.08 ± 3.30 3.56 ± 0.92 4.70 ± 1.38 3.56 ± 0.39

14 11.18 ± 2.15 6.88 ± 1.00 12.43 ± 1.32 2.89 ± 0.68 5.53 ± 0.82 2.89 ± 0.34

15 5.44 ± 0.91 3.92 ± 0.55 8.53 ± 1.40 1.95 ± 0.74 3.14 ± 0.51 1.95 ± 0.78

16 7.94 ± 1.01 4.80 ± 0.96 13.55 ± 2.16 2.64 ± 0.77 3.53 ± 0.72 2.64 ± 0.95

17 10.9 ± 1.36 5.15 ± 0.94 15.14 ± 3.31 2.98 ± 0.88 4.21 ± 1.04 2.98 ± 0.76

18 8.95 ± 2.40 6.38 ± 1.12 14.92 ± 3.98 4.31 ± 1.41 6.45 ± 1.22 4.31 ± 0.99

62

Table 3. Brittleness

Food I platen [kg] ± SD I cone [kg] ± SD I blade [kg] ± SD

1 9.25 ± 1.56 1.62 ± 0.46 1.60 ± 0.15

2 6.29 ± 2.93 1.65 ± 0.09 1.55 ± 0.10

3 2.68 ± 0.34 1.79 ± 0.13 1.55 ± 0.15

4 9.86 ± 2.42 1.56 ± 0.39 1.61 ± 0.13

5 8.86 ± 3.41 1.80 ± 0.19 1.55 ± 0.11

6 7.30 ± 0.89 1.71 ± 0.02 1.65 ± 0.18

7 8.74 ± 6.81 4.89 ± 1.81 1.64 ± 0.12

8 3.28 ± 0.91 1.24 ± 0.27 1.63 ± 0.23

9 14.11 ± 1.72 1.72 ± 0.18 1.58 ± 0.13

10 12.53 ± 2.05 1.40 ± 0.47 1.72 ± 0.08

11 14.51 ± 1.19 1.76 ± 0.18 1.71 ± 0.02

12 11.19 ± 2.87 1.76 ± 0.12 1.66 ± 0.11

13 11.49 ± 8.10 1.19 ± 0.31 1.69 ± 0.10

14 8.16 ± 1.96 1.41 ± 0.30 1.70 ± 0.10

15 4.08 ± 0.94 1.20 ± 0.36 1.72 ± 0.16

16 7.09 ± 1.68 1.30 ± 0.34 1.65 ± 0.07

17 8.25 ± 1.23 1.47 ± 0.31 1.64 ± 0.10

18 5.52 ± 2.32 1.75 ± 0.13 1.67 ± 0.09

Table 4. Fragility

Food I platen [kg/s] ± SD I cone [kg/s] ± SD I blade [kg/s] ± SD I cat [kg/s] ± SD

1 21.43 ± 8.69 6.40 ± 3.18 14.77 ± 4.08 2.43 ± 0.66

2 13.61 ± 2.65 8.02 ± 1.41 12.38 ± 1.39 1.80 ± 0.60

3 70.28 ± 25.12 11.20 ± 1.00 9.75 ± 3.14 2.82 ± 0.28

4 15.82 ±6.43 7.34 ± 2.70 12.96 ± 1.12 2.23 ± 0.35

5 10.89 ± 5.62 10.44 ± 2.62 15.20 ± 3.03 1.50 ± 0.55

6 9.03 ± 1.31 6.48 ± 0.64 14.21 ± 3.20 1.91 ± 0.65

7 19.78 ± 9.16 12.53 ± 3.75 14.46 ± 2.70 2.50 ± 0.13

8 7.32 ± 2.43 5.60 ± 1.35 8.53 ± 2.42 1.21 ± 0.35

9 16.13 ± 4.43 6.70 ± 1.37 15.60 ± 1.62 2.35 ± 1.12

10 16.95 ± 8.76 5.42 ± 1.07 18.21 ± 2.49 2.16 ± 0.16

11 29.12 ± 12.81 9.13 ± 1.95 17.62 ± 4.19 2.13 ± 0.67

12 16.44 ± 5.42 7.51 ± 1.13 12.05 ± 3.96 2.04 ± 0.49

13 30.67 ± 3.41 4.73 ± 0.91 12.70 ± 3.75 2.02 ± 0.21

14 23.12 ± 7.27 6.23 ± 1.00 15.68 ± 2.40 1.83 ± 0.30

15 5.04 ± 1.32 4.62 ± 1.68 6.52 ± 3.25 1.32 ± 0.60

16 12.69 ± 3.00 5.71 ± 1.02 10.65 ± 1.60 1.68 ± 0.52

17 15.40 ± 3.64 5.44 ± 0.52 13.12 ± 2.87 1.52 ± 0.47

18 11.79 ± 3.20 14.99 ± 4.61 23.96 ± 5.66 2.31 ± 0.69

63

Table 5. Chewiness

Food I platen ±

SD I cone ± SD

I blade ±

SD I cat ± SD

1 7.85 ± 1.72 2.30 ± 0.37 1.50 ± 0.28 1.74 ± 1.66

2 6.59 ± 0.83 1.37 ± 0.13 0.63 ± 0.20 0.58 ± 0.35

3 27.57 ± 3.25 2.27 ± 0.77 1.15 ± 0.25 3.22 ± 1.57

4 8.98 ± 2.99 0.88 ± 0.26 0.67 ± 0.14 0.61 ± 0.32

5 5.82 ± 2.05 1.54 ± 0.47 1.26 ± 0.42 1.00 ± 0.99

6 7.41 ± 1.22 2.52 ± 0.80 1.35 ± 0.36 2.20 ± 2.08

7 8.99 ± 2.34 18.81 ± 4.39 0.94 ± 0.24 2.52 ± 1.43

8 3.17 ± 0.41 0.86 ± 0.38 0.79 ± 0.19 0.49 ± 0.46

9 16.93 ± 2.21 3.73 ± 0.77 1.72 ± 0.37 3.52 ± 3.44

10 9.12 ± 0.78 1.53 ± 0.65 1.30 ± 0.55 1.83 ± 0.79

11 12.12 ± 1.57 2.05 ± 0.66 1.59 ± 0.42 1.49 ± 0.25

12 13.17 ± 1.84 2.08 ± 0.19 1.22 ± 0.22 1.26 ± 0.47

13 17.24 ± 1.71 3.03 ± 0.90 1.13 ± 0.69 1.45 ± 0.57

14 7.61 ± 1.40 1.97 ± 0.56 1.31 ± 0.34 1.19 ± 0.46

15 5.36 ± 0.65 1.28 ± 0.52 1.29 ± 0.57 1.28 ± 1.09

16 6.64 ± 0.92 1.68 ± 0.65 0.72 ± 0.32 1.28 ± 1.02

17 7.45 ± 1.06 1.78 ± 0.74 0.83 ± 0.25 0.93 ± 0.47

18 6.70 ± 1.60 1.38 ± 0.43 0.73 ± 0.16 1.41 ± 1.24

Table 6. Ingestion speed

Food Ingestion speed [g/min]

cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8

1 4.99 4.89 7.43 4.61 4.05 5.20 7.91

2 5.44 4.18 7.02 3.06 4.88 3.97 5.33 3.76

3 10.06 8.27 10.36 5.44 5.29 7.23 9.91

4 7.70 5.15 8.43 2.89 7.50

5 6.90 4.71 10.28 4.03 3.83 5.22 8.70

9 9.71 6.63 11.84 7.33 6.54 6.71 9.79

11 6.32 6.28 8.02 5.10 7.50 4.21 7.43 3.98

12 6.14 4.91 7.62 4.49 5.56 5.17 7.14 4.98

13 5.70 5.20 8.12 5.42 3.98 4.79 8.12 5.66

14 6.85 4.35 6.56 5.75 4.84 4.53 5.56 5.00

16 7.73 8.35 8.32 5.18 7.68 5.98 6.67 5.51

18 10.46 8.95 12.60 6.16 3.47 5.26 10.84 5.24

Table 7. Biting + chewing rate

Food Biting + chewing rate [rpm]

cat 1 cat 2 cat 3 cat 4 cat 5 cat 6 cat 7 cat 8

1 3.93 0.97 2.86 0.00 1.79 2.03 1.58

2 4.29 1.64 5.58 0.00 0.97 6.32 3.16 4.44

3 22.00 9.73 14.00 2.14 12.41 12.56 13.55

4 12.00 9.15 8.33 9.03 4.29

5 11.74 16.36 20.00 4.68 22.03 16.55 11.67

9 5.63 1.30 11.54 1.46 5.00 9.33 7.74

11 9.80 4.90 12.31 5.00 12.27 9.04 2.93 12.77

12 4.80 3.87 9.00 2.61 6.67 5.17 1.40 12.79

13 12.22 14.24 9.47 2.14 8.57 11.25 11.35 7.92

14 2.73 1.74 5.22 4.53 0.95 7.16 3.33 9.00

16 4.50 0.00 16.22 1.02 3.00 1.18 0.00 13.09

18 0.00 3.43 5.00 0.00 0.00 4.07 4.14 6.55

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