Nutritional Considerations in the Pediatric Dog:
Dietary and Developmental Relationships
A.J. Reynolds, DVM, PhD, DACVN
Purina Resaerch Report
Spring 2000

Approximately 30% of puppy mortality occurs during the first 14 days of life(1). Many of these deaths result from inadequate nutrition or the inability of the gastrointestinal tract (GIT) to adequately digest and absorb nutrients(2). The nutritional state experienced during prenatal and postnatal development and growth can have a major influence on longevity and the incidence of diseases later in life(3,4). Thus, understanding how, why and when the GIT changes during development may help owners and veterinarians provide diets that best meet the needs and digestive abilities of growing puppies and kittens during each stage of development.

Prenatal and Neonatal Development
The signals that regulate the differentiation and development of the fetal GIT are not well understood. It is likely that factors exist in the amniotic fluid that may play a role in this process. Gut peptides are found in the fetal human GIT within the first trimester and in the amniotic fluid by the second trimester (5). In porcine and ovine feti, GIT development was impaired when the swallowing of amniotic fluid was prevented (6,7). Compared to controls, these animals showed a decrease in the weight of their small intestine, pancreas and liver and a generalized thinning of the gut wall throughout the length of the GIT (6,7). Other factors, including cortisol, insulin and numerous other hormones, present in both the fetal and maternal circulation also may have significant effects on GIT development. Although there have been very few studies examining the prenatal development of the GIT in dogs and cats, some brush border enzymatic activity and nutrient transport activity is developed by the time of parturition (8).

Birth to Weaning
At birth, the GIT undergoes perhaps the most drastic change in function of any organ system except the lungs. During the first 24 hours, the canine small intestine nearly doubles in weight (9). At this time, the GIT must take over from the placenta the huge task of transferring nutrients from the outside world to the neonatal circulation. Since neonatal puppies and kittens have very small energy and glucose reserves, failure to make this accommodation becomes a serious if not fatal problem in a matter of hours.

The normal neonatal GIT is fully capable of digestion and absorption of its primary substrate, mother's mild. Many of the brush border enzymes found in the mature GIT are present to facilitate the final stages of digestion and thus absorption. The activity of these enzymes increases markedly just before parturition and so premature animals may experience digestive difficulties (2).

The neonatal GIT is not well suited for ingesta other than milk. Newborn puppies lack certain pancreatic enzymes and the muscularis layer of their small intestine is about 50% thinner than that found in adult dogs. (2,10). Some of the brush border enzymes, particular ly the alphaglycosidases, are not well developed and this can cause problems if sugars such as sucrose or maltose are used in homemade mild replacers.

While the neonatal GIT may have difficulty handling foods other than mild, it is highly specialized for mild digestion and absorption. Not surprisingly, the changes which occur in the developing GIT are well matched to changes in the composition and volume of the mild with which it is presented. The first mild, colostrum, is rich in protein, immunoglobulins, hormones and other factors which promote hypertrophy and hyperplasia of the neonatal GIT. Puppies fed mild replacer instead of colustrum experience a much smaller increase in intestinal mass during the first 24 hours of life. (2)

The ability to internalize large molecules such as proteins persists up to two weeks after birth in many species. (11) In puppies, this may help compensate for inadequate activities of pancreatic proteases(2) which are secreted in only small amounts during the first one to two weeks of life.(10) Neonatal puppies also secrete very little pancreatic lipase but this is compensated for by secretion of gastric lipase. As the concentration of fat in mild increases over time, the secretion of pancreatic lipase also increased.(10)

Weaning and Beyond
From the second week to the seventh week of life, there is multi-fold decrease in mild intake as a percent of body weight. Similarly there is a three-fold increase in solid food intake as a percent of body weight from the third week to the seventh week.(2) By three weeks of age, the puppy's GIT will have undergone considerable changes. The thickness of the gut wall will have nearly doubled primarily due to hypertrophy of the tunica muscularis. This will facilitate the passage of solid ingesta along the lumen of the gut. (2) The pancreas will have developed adequate capacity to produce digestive enzymes as well as antibacterial factors.(10) The introduction of solid food provides both a source and a substrate for bacterial growth and these factors take over from those found in mild to help establish normal GI microflora.

In later life, the ability to change digestive function varies among species in accordance with natural variation in the diet.(2) the cat, which is an obligate predator, is less able to vary its pancreatic and GIT enzyme activity than is the more omnivorous dog. (2,10,12) Dogs also possess a tremendous capacity to adapt their GIT function over an enormous range of energy requirements. For most dogs, the largest demand on the GIT for processing nutrients occurs during growth. A weaned puppy may require two to three times the energy per unit body weight of a sedentary adult dog. (13) If that puppy is a bitch that later whelps a large litter, her energy requirement may return to that same three times maintenance she experienced as a puppy.(13) If she is a sled dog running 100 miles a day in subzero conditions, her GIT will need to process foods to meet her energy needs which reach an incredible eight times maintenance. (14)

Feeding the Neonatal Puppy
All of these developmental changes are important to consider when feeding young puppies. Puppies should increase their bodyweight about 10% each day during the early neonatal period. If puppies require nutritional intervention before three weeks of age, their GIT is not yet capable of handling solid food. Pups this age should be fed mild replacers which mimic canine mother's milk in nutrient concentration (78% water, 8% protein, 10% fat, 1.2-1.4 Kcal/gm) and digestibility. (15) The ingredients should ideally be milk-based (i.e., casein or whey) for the protein source, lactose for the carbohydrate, and milk fat or at the least emulsified fats for the lipid source. If tube feeding is necessary, puppies should receive about 20-26 Kcal/100 gm body weight, divided into several feedings. (15) Commercial foods balanced for the needs of growing puppies should be introduced beginning at about three weeks of age. Dry foods should be mixed with warm water and provided in shallow bowls several times each day. During this period, puppies should continue to gain weight daily and this can be used as a measure of adequate energy intake. Puppies that lose or merely maintain their body weight are not receiving enough calories and may require supplementation with mild replacer or a more energy dense solid food.


References:
  1. Poffenbaarger EM, Olson PN, Ralston SL, Chandler MI. Canine Neonatology Part II: Disorders of the Neonate.
    Compd Cont Edu Pract Vet 1991; 13:25-37.
  2. Buddington RK Paulsen DB. Development of the canine and feline gastrointestinal tract. In Recent Advances in Canine and Feline Nutrition Vol II. GA Reinhart and DP Cary eds.
    Orange Frazier Press Wilmington 1998. Pp195-213.
  3. Langley-Evans SC, Phillips GJ, Jackson AA. Fetal exposure to low protein maternal diet alters the susceptibility of young adult rats to sulfur dioxide-induced lung injury.
    J. Nutr. 1997; 127: 202-209.
  4. Newberne PM. Animal models for investigation of latent effects of malnutrition.
    Am J Dis Child 1975; 129:574-577.
  5. Lucas A, Bloom Sr, Green AA. Gastrointestinal peptides and the adaptation to extrauterine nutrition.
    Can J Physiol Pharmacol 1985;63:527-537.
  6. Avila CG; Harding R. The development of the gastrointestinal system in fetal sheep in the absence of ingested fluid.
    J Pediatr Gastroenterol Nutr 1991 Jan;12(1):96-104.
  7. Mulvihill SJ; Stone NM; Fonkalsrud EW; Debas Trophic effect of amniotic fluid on fetal gastrointestinal development.
    J Surg Res 1986 Apr;40(4):291-6.
  8. Buddington RK, Nutrition and Ontogenetic development of the intestine.
    Can J Physiol Pharmacol 1980; 72:251-259.
  9. Heird WC, Schwarz SM, Hansen IH. Colostrum induced enteric mucosal growth in Beagle puppies.
    Pediatric Res 1984; 18-512-15.
  10. Elnif J. Buddington RK. Adaptation and development of the exocrine pancreas in cats and dogs. In Recent Advances in Canine and Feline Nutrition Vol II. GA Reinhart and DP Carey eds.
    Orange Frazier Press Wilmington 1998: Pp 217-29.
  11. 11. Clarke RM, Hary RN. Structural changes in the small intestine associated with the uptake of polyvinyl pyrrolidone by the young ferret, rat, guinea-pig, cat and chicken.
    J. Physiol 1970; 209:669-87.
  12. Ballesta MC, Manas M, Mataix FJ, Martinez-Victoria E, Siequer I. Longer term adaptation of pancreatic response by dogs to dietary fats of different degrees of saturation: olive and sunflower oil. Brit.
    J. Nutr. 1990; 64:487-496.
  13. National Rresearch Council Subcommittee on Dog Nutrition. Nutrient Requirements of Dogs.
    1985.
    National Academy Press. Washington DC. Pp 2-9.
  14. Hinchcliff KW, Reinhart GA, Burr JR, Schrier Cj, and Swenson RA. Metabolizable energy intake and sustained energy expenditure of Alaskan sled dogs during heavy exertion in the cold.
    Am. J. Vet. Rews. 1997 Dec; 58(12).
  15. Lawler DF, Chander ML. Indications and techniques for tube feeding puppies.
    Canine Pract 1992;17:13-16.