Slowly Fermentable Grains May

Reduce Metabolic Heat and

Ameliorate Heat Stress in Grain-Fed

Sheep

P.A. Gonzalez-Rivas, K. DiGiacomo, V. M .Russo*,

B.J. Leury, J.J. Cottrell, and F.R. Dunshea

Faculty of Veterinary and Agricultural Sciences, The University

of Melbourne, Parkville, Victoria, Australia.

*Department of Economic Development, Jobs, Transport and

Resources, Ellinbank, Victoria, Australia.

INTRODUCTION

• Ruminants can be more susceptible to Heat stress

(Coppock, 1985; Goetsch and Johnson, 1999; Roy and Collier, 2012).

• Rapidly fermentable grains (wheat); digestive

disorders, laminitis and higher metabolic heat

production (Nocek, 1997; Oetzel and Smith, 2000; Stone, 2004, Grant

and Albright, 1995; Brosh et al., 1998; Mader et al., 1999).

• Slowly fermentable grains (corn); better utilization of

ME and reduction of the heat from fermentation

(Ørskov, 1986; Owens et al., 1986).

Objectives

• To characterise the in vitro gas production kinetic

parameters of wheat and corn grains.

• To compare physiological parameters of sheep fed

either slowly or rapidly fermentable grain-based diets

under heat stress conditions.

Hypotheses

• Wheat has a faster rate of in vitro fermentation than

corn.

• Feeding slowly fermentable grains can reduce

the impact of heat stress in grain-fed sheep.

MATERIAL AND METHODS

In Vitro Experiment

• 28 replicates of 1g of 1mm-

ground wheat ASW 10% (70%

starch) and corn (74% starch).

• Buffered rumen fluid (Kansas-

State buffer pH 6.8) ratio 1:3

• Gas recording modules

ANKOMRF Wireless system

every 5 minutes

• Incubated for 24 h at 39⁰C

www.ankom.com

MATERIAL AND METHODS

In Vivo experiment

Experimental Design

Randomized Control Trial

Animals

– 22 Merino X Poll Dorset crossbred wether lambs.

– 11-12 mo

– 41.2±2.4 Kg BW

– Fleece cover 3 cm

Diets

• Control - rapidly fermentable diet “Wheat Diet”

50% crushed wheat grain + 50% of oaten/lucerne

chaff

• Intervention - slowly fermentable diet “Corn Diet”

50% crushed corn grain + 50% of oaten/lucerne

chaff

Both: 4% DM Balanced Supplement

12.7 % CP, 11.9 MJ ME/Kg DM,

23.8% NDF and 37.9% starch

Fed three times a day (0900, 1300,1700h)

MATERIAL AND METHODS

Accl.

(15 d)

• Acclimation feeding (1.5 x Maintenance requirements)

Period 1

(P1,7d)

• Thermoneutral (18 to 21⁰C and 40-50% RH, 24 h)

• Restrictive feeding (1.3 x Maintenance requirements)

Period 2

(P2, 7d)

• Heat stress (38⁰C/ 30% RH; 0900 to 1700 h, 28⁰C/50% RH;1700 to 0900 h)

• Restrictive feeding (1.3 x Maintenance requirements)

Period 3

(P3,7d)

• Heat stress (38⁰C/ 30% RH; 0900 to 1700 h, 28⁰C/ 50% RH;1700 to 0900 h)

• Acclimation feeding (1.5 x Maintenance requirements)

MATERIAL AND METHODS

• Respiration rate (RR)

• Rectal temperature (RT)

• Left and right flank skin temperature (LST and

RST)

• 0900, 1300, 1700 and 2100h during the experiment.

• Feed /water intake

PHYSIOLOGICAL

MEASUREMENTS

STATISTICAL ANALYSIS

In vitro gas production

• Gas production curve was fitted to the Gompertz

model. REML using the statistical package GenStat

(GenStat release 14; VSN International Ltd., Hemel

Hempstead, UK)

Y = A + C exp (-exp (-B(X-M)))

Where:

• B = Rate of gas production (mL h-1)

• M = Time at which the maximum rate of gas production is

reached (h)

• C = Maximum gas produced (Max gas mL/g DM)

• A = Y-intercept

STATISTICAL ANALYSIS

In vivo experiment

• Restricted Maximum Likelihood (REML) analysis

procedure for GenStat

• True differences between left and right flank skin

temperature were estimated by conducting a t-Test.

Corn had slower rate of gas production (ml gas h-1)

than wheat (P<0.001). Wheat reached the maximum

rate of gas production earlier than corn (P<0.001)

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14 16 18 20 22 24

Ga

s P

rod

uct

ion

(m

L/g

DM

)

Time (h)

Corn (74% Starch)

Wheat (70% Starch)

Max Rate 8.7 h

Max Rate 6.8 h

• Protein Matrix

• Amylose content

• Resistance to bacterial enzymatic

attack

Heat stress increased RR (P<0.001) and

corn-fed sheep had lower RR across periods

(P<0.001)

20

40

60

80

100

120

140

160

180

200

9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00

Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)

Res

pir

ati

on

Ra

te, b

rea

ths

per

min

ute

Corn

Wheat

Max Heat Max Heat

Corn -fed sheep showing lower RR at 38 C⁰/30% RH

Corn-fed sheep Wheat- fed sheep

Heat stress increased RT (P<0.001),

Corn-fed sheep had lower RT at high ambient

temperature (P<0.001).

39.0

39.1

39.2

39.3

39.4

39.5

39.6

39.7

39.8

39.9

40.0

9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00

Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)

Rec

tal T

emp

era

ture

, ⁰C

Corn

Wheat

Max Heat Max Heat

Skin temperature increased with heat stress (P< 0.001)

Corn- fed sheep had lower skin flank temperature (P<0.001)

LST was higher than RST (P<0.001)

38.2

38.4

38.6

38.8

39.0

39.2

39.4

39.6

9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00 9:00 13:00 17:00 21:00

Thermoneutral (P1, 1.3 x M) Heat Stress (P2, 1.3 x M) Heat Stress (P3, 1.5 x M)

Sk

in T

emp

era

ture

, ⁰C

LST Corn

RST Corn

LST Wheat

RST Wheat

Max Heat Max Heat

Wheat-fed sheep had larger difference between left

and right flank skin temperature (P<0.001)

Left Flank Right Flank

http://bvetmed1.blogspot.c

om.au/2013/03/ruminant-

abdomen-lecture-157.html

(Laue and Petersen, 1991;

Montanholi et al., 2008)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

Corn Wheat

Tem

per

atu

re, ⁰C

Difference left -right flank skin

temperature

CONCLUSION

• Corn grain had slower fermentation rate than wheat

grain

• Feeding a corn-based diet reduced the total heat

increment.

• Corn grain diet ameliorated the physiological

responses negatively affected by HS in grain-fed

sheep compared to dietary wheat.

• Higher feed intake increased the thermal load of the

animals under HS.

ACKNOWLEDGMENTS

• Faculty of Veterinary and Agricultural Sciences,

The University of Melbourne

• Animal Science group, animal house Parkville

and Dookie campus staff

Dr. Surinder Chauhan, Ms Maree Cox, Mr Evan Bittner, Ms

Shannon Holbrook, Dr. Michelle Henry, Ms Paula Giraldo, Mr

Ashley Gabler, Mr Frank O’Connor.