canine feeding & nutrition guide
TRANSCRIPT
IntroductionAlthough canines (dogs) are
classified as carnivores, they like avariety of foods. Different food-stuffs are mixed to provide abalanced diet that meets the dog’snutrient requirements at a specificstage of life. Whether commer-cially manufactured or homeprepared, dogs need to consume anutritionally complete diet daily tokeep them physically fit andhealthy. Like humans, dogs haverequirements for essential foodconstituents such as carbohydrates,fats, proteins, vitamins, minerals,and water.
NutrientsCarbohydrates. Although
there is no known dietary require-ment for carbohydrates in dogs,they are an excellent source ofenergy. Cereal grains such as corn,barley, rice, and wheat have a highcontent of starch, which provides asource of energy in most commer-cial dog foods. Milk contains alarge amount of the carbohydratelactose, but it may cause diarrheain some dogs. On the other hand,foodstuffs such as beet pulp, whichcontains high levels of insolublecarbohydrates (fiber), helps withthe prevention and treatment ofdiarrhea. Furthermore, fiber, whichis composed of cellulose, hemicel-lulose, lignin, and pectin, alsodecreases the retention time of
feces in the large intestine, hence,helping to prevent and treatconstipation. An increase in theamount of fiber in the diet can alsobenefit overweight dogs bymaintaining the animal’s sensationof fill, hence, decreasing thecaloric intake.
Fats. The most concentratedsource of energy in the diet is fat.This nutrient consists of glyceroland fatty acids, which can besaturated or unsaturated. However,the dog requires essentially linoleicand arachidonic acid, both ofwhich must be provided in the diet.Fats used commercially includecottonseed oil, hydrogenatedvegetable oil, poultry fat, lard, andtallow. Furthermore, fats contributeto palatability and texture of diets,and carry the fat-soluble vitaminsA, D, E and K. The most prevalentproblem related to fat is over-consumption and obesity. How-ever, dogs fed a low fat diet veryoften will have a dull coat and dryskin. Therefore, a balanced dietcustom-tailored for the specific lifecycle of the dog is the best solutionto prevent fat-related problems.
Proteins. One of the mostimportant nutrients in the diet isprotein. However, what dogs reallyneed are the amino acids that makeup the protein. Of the 20 aminoacids required, dogs can synthesizehalf of them, while the remainingones must be consumed. The latterones, called essential amino acids,
include arginine, histidine, isoleu-cine, leucine, lysine, methionine,phenylalanine, threonine, tryp-tophan, and valine. Since eachprotein contains different amountsof amino acids, some proteins arebetter than others. Foodstuffs ofanimal origin such as beef,chicken, lamb, and turkey have abetter protein quality than food-stuffs of plant origin such assoybean meal and corn. Mostcommercial diets provide adequateprotein sources for the differentlife stages of the dog.
Vitamins. Vitamins areorganic compounds that areessential for normal metabolism.They can be classified as fat-soluble or water-soluble. VitaminsA, D, E and K are fat-soluble,while B-complex vitamins such asthiamin (B1), niacin, riboflavin(B2), pantothenic acid (B5), pyri-doxine (B6), folic acid, cobalamin(B12), and biotin are water-soluble.Vitamin C (ascorbic acid) is alsoclassified as water-soluble. Theseorganic substances are naturallypresent in small amounts in mostfoodstuffs, hence, the commercialmanufacture of vitamin supple-ments for dogs. It is worth caution-ing that because fat-solublevitamins are commonly stored infat tissue cells within the body,they pose a big threat if over-supplemented. Water-solublevitamins, on the other hand, areeasily eliminated from the body
via the urine, hence, a minimal riskof toxicity.
Minerals. Like vitamins,minerals play very important rolesin physiology and metabolism.These inorganic nutrients aredivided into macro and microcategories. The macro-minerals areneeded in larger amounts in thediet than the micro-minerals (traceelements). However, both performmany different functions includingbone formation, blood clotting,transport of oxygen in the blood,muscle contraction, and nerveimpulse transmission. Calcium andphosphorus are the major mineralsinvolved in the formation of boneand cartilage in the body. Le-gumes, dairy products, and bonescontain large quantities of calcium,while muscle and organ tissues arehigh in phosphorus. Therefore,minerals must be added in order toprovide the correct calcium tophosphorus ratio (1.2:1) in the dietproper. A deficiency, an excess, oran imbalance of these minerals,can cause severe skeletal deformi-ties. Other important macro-minerals include magnesium,potassium, sodium, and chloride.Important micro-minerals amongothers are copper, iodine, iron,manganese, selenium, and zinc.
Water. Water is the mostimportant of all nutrients. It helpsto regulate the body’s temperature,and, as the principle constituent ofblood, transports nutrients to thedifferent body tissues, thus remov-ing metabolic-end products fromthe dog’s system. Furthermore,some chemical reactions within theanimal cell require the addition orsubtraction of water. Therefore, thedog requires ad libitum water ofthe highest quality.
Digestion and AbsorptionThe dog has a monogastric
gastrointestinal tract (Figure 1) thatincludes the mouth, esophagus,stomach, small intestine, and largeintestine. This tract works with theaid of the salivary glands, pan-creas, liver, and gallbladder tobreak down the large forms ofnutrients in the food into simpleforms that the body can absorb andutilize.
Mouth and Esophagus. Thedigestive process begins in themouth with the mechanical break-down of food into smaller particlesthrough the action of the teeth (28in puppies and 42 in adult dogs)that line the upper and lower jaws.Saliva secreted by the salivaryglands aids to lubricate the food.Unlike humans, the enzymeptyalin, an alpha-amylase, is notfound in the saliva of dogs.
After swallowing, food movesrapidly through the esophagus tothe stomach. The cardiac sphincter,which is located at the base of the
Figure 1. The gastrointestinal tract of the dog.
stomach, relaxes to allow food toenter from the esophagus into thestomach, and then immediatelycloses to prevent the acidic stom-ach contents from backing up intothe lower esophagus.
Stomach. The gastric juice,which is produced by the cells ofthe stomach, contains mucus,hydrochloric acid, pepsinogen (theinactive form of the enzymepepsin), and the enzyme gastriclipase. Hydrochloric acid influ-ences the conversion of pepsino-gen to its active form, pepsin,which partially hydrolyzes proteinto smaller polypeptides while inthe stomach. The enzyme gastriclipase, which plays a minor role inthe digestion of fats, hydrolyzestriglycerides into fatty acids andglycerol. The resulting chyme (asemifluid mass of partially di-gested food and digestive juices)then passes into the small intestinevia the pyloric sphincter that closesinstantly to prevent reflux backinto the stomach.
Small Intestine. The digestionand absorption of nutrients in thebody occurs primarily in the small
Pancreas SmallIntestine
Anus
LargeIntestine
Mouth
Esophagus
StomachLiver
GallBladder
CecumVilli
Canine Feeding and Nutrition 3
intestine. The duodenum (thesection of the small intestineclosest to the stomach) is mainlyresponsible for digestion, while thejejunum (the middle section of thesmall intestine) and the ileum (theterminal section of the smallintestine) are mainly responsiblefor absorption. To digest carbohy-drates, fats, and proteins, thepancreas and the walls of the smallintestine secrete into the intestinallumen the following enzymes:
• pancreatic amylaseconverts starch into maltose
• intestinal maltaseconverts maltose into glucose
• intestinal lactaseconverts lactose into glucoseand galactose
• intestinal sucraseconverts sucrose into glucoseand fructose
• pancreatic lipaseconverts triglycerides intomonoglycerides and fatty acids
• intestinal lipaseconverts triglycerides intoglycerol and fatty acids
• trypsin and chymotrypsin(secreted by the pancreas)converts proteins and polypep-tides into peptides
• pancreatic carboxypeptidaseconverts peptides into smallpeptides and amino acids
• intestinal aminopeptidaseconverts peptides into aminoacids
It should be mentioned that bile,which is secreted by the liver andstored in the gallbladder, emulsi-fies fats to provide sufficientsurface area for efficient digestion.
As end products of digestionare made available, they areabsorbed across the intestinal wallinto the body. The surface areaavailable for absorption is in-creased by small fingerlike projec-tions called villi that cover theintestinal wall. Each cell lining thesurface of each villus is coveredwith hairlike projections calledmicrovilli. As nutrients travelthrough the small intestine, theyare trapped in the villi of theintestinal wall and absorbedthrough the microvilli into thelining cells. The nutrients absorbedthen pass into the interior of thevilli that contain veins, arteries,capillaries, and lymphatic vesselsfor transport to the tissues of thebody.
Large Intestine. The contentsof the small intestine enter thelarge intestine through theileocecal valve, whichthen closes to preventmaterial from backinginto the ileum of thesmall intestine. Thelarge intestine, whichincludes the cecum,colon, and rectum, isresponsible mainly forthe bacterial digestionof dietary fiber andabsorption of waterand minerals. Further-more, the bacterialpopulation present inthe colon also pro-duces some vitaminsand various gases.Feces, which consistsof undigested food,water, sloughed cells,digestive secretions,and bacteria, thenpasses into the rectum
and is excreted through the analcanal.
Body Tissue MetabolismCatabolism. Tissue cells break
down nutrients through thousandsof chemical reactions. Thesereactions release high-energyelectrons that are received andcarried by coenzymes such asnicotinamide adenine dinucleotide(NAD+) and flavin adenine di-nucleotide (FAD+). When thesecoenzymes accept two high-energyelectrons, they pick up two hydro-gen (H) ions to form NADH + H+
and FADH2, respectively. Wheneach pair of electrons are passedalong a sequence of linked reac-tions in the respiratory chain(Figure 2), they generate adenosinetriphosphate (ATP). Just as auto-mobiles require gasoline for fuel,body tissue cells require ATP
NADH + H+
Flavin Mononucleotide
Coenzyme Q
ADP + Pi
ATP
Iron-Sulfur Protein
Iron-Sulfur Protein
FADH2
Cytochrome b
Iron-Sulfur Protein
Cytochrome c1
Cytochrome c
Cytochrome a
Cytochrome a3
O2
ADP + Pi
ATP
ADP + Pi
ATP
Figure 2. ATP generation in the respiratorychain of the mitochondria.
(Figure 3) to sustain life. When thebonds between the phosphates ofATP break, they release the storedenergy to power biosynthesis andbiological work. The completebreakdown of nutrients for energyoccurs through biochemicalpathways such as glycolysis,β-oxidation, transamination,oxidative deamination, and thecitric acid cycle.
Anabolism. While some tissuecells are breaking down nutrientsto obtain energy, other tissue cellsare synthesizing them. When thebody has an excess of nutrients,biosynthesis takes place. Biosyn-thetic pathways that are active intissue cells include gluconeogen-esis, glycogenesis, lipogenesis,ketogenesis, transamination, andprotein synthesis. The sequence ofamino acids in a protein is speci-fied by the sequence of nitrog-enous bases (adenine (A), thymine(T), guanine (G), and cytosine (C)in a deoxyribonucleic acid (DNA)molecule. However, the sequenceof bases in a DNA molecule(Figure 4) has to first be tran-scribed to another molecule calledmessenger ribonucleic acid(mRNA). The mRNA, that is
Figure 3. ATP is required by body tissue cells to sustain life.
amino acids are inserted at theircorresponding site on the mRNA,and subsequently, attached to thegrowing polypeptide chain. Thisprocess of protein synthesis entailsinitiation, elongation, and termina-tion.
The balance between break-down and synthesis of nutrients isregulated by hormones and otherfactors. Among the regulatoryhormones is insulin, which issecreted by the pancreas to reducethe amount of glucose in the blood.When the pancreas fails to producethe hormone, Type I diabetesmellitus occurs. On the other hand,when insulin levels are adequatebut body tissue cells have diffi-culty uptaking glucose, Type IIdiabetes mellitus occurs. This typeof diabetes is almost alwaysassociated with obesity, the mostcommon form of malnutrition indogs in the United States. How-ever, other factors such as breed,reproductive status, level ofactivity, and type of diet may affectobesity in dogs. Therefore, anutritional management programmust be developed and imple-mented to effectively manageobesity and treat diabetes mellitus.Furthermore, because of the largevariety of dog food availabletoday, owners must have somebasic knowledge of nutrition inorder to select the appropriate dietfor a particular stage of life, levelof activity, and health status.
Guidelines for SelectingFoods and Feeding Dogs• Make sure that the label in
commercially manufacturedfoods has the Association ofAmerican Feed ControlOfficials (AAFCO) guarantee.
• Be certain that the food has anexpiration date.
Figure 4. In the double-strandedDNA, adenine pairs with thyminewhile guanine pairs with cytosine.
complementary to the DNA,except that the mRNA containsuracil (U) instead of thymine, thencarries the genetic informationfrom the nucleus to the ribosomesof the cell. On these organelles, the
NH2
N
N
N
N
C C
CCH
H H
H
O
HO OH
CH2 O P O P O P OH
OH OH OH
O O O
Adenine
Ribose
4 Alabama Cooperative Extension System
• Look for meat (beef, chicken,lamb or turkey) as the firstingredient, rice as the maingrain in the formula, andmixed tocopherols (vitamin E)as preservatives. It’s worthmentioning that foods pre-served with vitamins have ashorter shelf life than foodspreserved with butylatedhydroxyanisole (BHA) orbutylated hydroxytoluene(BHT). However, according tosome research, very high dosesof these chemicals may causecancer.
• Store food in a sealed con-tainer in a cool, dry place.
• If the dog has a special dietaryrequirement that cannot be metby commercial foods, considerfeeding homemade diets.
• Feed the dog according tocorrect body weight andcondition, and consider factorssuch as growth, adult mainte-nance, level of activity,
ConclusionLike humans, dogs require a
diet that contains the correctamounts of carbohydrates, fats,proteins, vitamins, minerals, andwater that provide sufficientenergy to meet the daily needs oftheir particular life cycle. Dietaryrequirements for dogs can varyaccording to breed, stage of life,level of activity, health status,living conditions (indoor oroutdoor), and season. If the doghas a good body weight andcondition, healthy skin and coat, isactive, and receives good marksfrom annual medical checkups(Figure 6), the owner has donewell. However, if the food iscausing problems, the owner cantake steps to correct matters bychanging food, having some testsdone on the dog, or make otheradjustments as necessary.
Figure 5. Puppies must consume colostrum (first milk)within the first 36 to 48 hours after birth.
gestation, lactation, and age.Use the National ResearchCouncil's (NRC) NutrientRequirements of Dogs (1985).
• When changing foods, mix1/4 of the new food to 3/4 ofthe old food, and increasegradually to prevent gastricupsets. Watch the dog's stool,weight, and coat while chang-ing foods.
• Feed adult dogs twice a day toprevent gorging on a singlemeal and to reduce the occur-rence of gastric upsets. Allowapproximately 20 minutes forthe dog to clean the bowl.
• Make sure that puppiesconsume colostrum (first milk)within the first 36 to 48 hoursafter birth (Figure 5). Theabsorption of colostral immu-noglobulins (antibodies) acrossthe intestinal wall decreasesthereafter, hence, reducing thechances of survival greatly.
• Make sure that the dog hasfresh and clean water at alltimes.
Figure 6. If the dog receives good marks fromannual checkups, the owner has done well.
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References
Animal Protection Institute (API). (1999). Buying Commercial Pet Food—A Checklist. In: What’sReally in Pet Food. Online July 23.
Case, L. P. (1999). The Dog: Its Behavior, Nutrition, and Health. Ames, Iowa: Iowa State UniversityPress.
Currie, W. B. (1988). Structure and Function of Domestic Animals. Stoneham, Massachusetts:Butterworth Publishers, Inc.
Gillespie, J. R. (1998). Animal Science. Albany, New York: Delmar Publishers, Inc.
Harper, H. A., V. W. Rodwell and P. A. Mayes. (1977). Review of Physiological Chemistry. Los Altos,California: Lange Medical Publications.
Insel, P., R. E. Turner and D. Ross. (2001). Nutrition. Sudbury, Massachusetts: Jones and BartlettPublishers, Inc.
National Research Council. (1985). Nutrient Requirements of Dogs. Washington, D.C.: NationalAcademy Press.
Zubay, G. L. (1983). Biochemistry. Reading, Massachusetts: Addison-Wesley Publishing Company, Inc.
Allow approximately 20 minutes for the dog to clean the bowl.
Energy extracted from food is essential for biological work.
Good body weight and a healthy skin and coat are indicators of wellness.
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A nutritionally complete diet keeps the dog physically fit and healthy.