Neonatal pediatric nutrition

Introduction

The post-birth period is a critical time for all animal species, and growth is a complex process encompassing interactions between genetics, diet and other environmental influences. Nutrition plays a significant role in the health and development of neonatal kittens and puppies, directly affecting their immune system, body composition, growth rate, and skeletal development. Diet is not only a controllable factor, it is perhaps the principal factor influencing health and disease in young animals. The objective when feeding pediatrics is to ensure they develop into healthy adults, and this article sets out how to attain the goals necessary for a successful neonate feeding plan. The aims are to achieve healthy growth, enhance development, minimize disease risk factors, and ensure optimal overall well-being. Additionally, proper nutrition will aid in optimizing trainability and immune function, and minimize obesity and the development of any orthopedic disease.

Neonates

The first two weeks of life are known as the neonatal period of cats and dogs, with the first week believed to be the most critical for survival (1,2). Due to high rates of morbidity and mortality, this period remains a major challenge for veterinary teams, breeders and owners. These rates range from 5.7-35% in dogs (3-6) and from 14-16% in cats (7,8). Newborn puppies and kittens are physiologically immature, with low levels of body fat; 1-2% as compared to 12-35% in adult dogs and cats. This immature status is termed altricial, meaning they are born immature and are completely dependent on their mother for survival (1,9). If the puppy or kitten is orphaned, their care will rely on foster parents until they are mature enough to be independent.

The first nutritional concern for newborns is that they receive colostrum immediately after birth (Figure 1). Produced by the mother during the first 24-72 hours after parturition, colostrum provides nutrients, water, growth factors, digestive enzymes and maternal antibodies. Most of the antibodies and other factors conveyed through the colostrum are in the form of large proteins; these are absorbed across the intestinal barrier, providing passive immunity to the neonate (1). However, the neonate's capacity to absorb these proteins is limited to the first 24-72 hours of life; after this point, continuation of colostrum provides no additional immunity to the neonate. Additionally, it is important to remember that the offspring can only receive protection from diseases for which the dam has been vaccinated or has contracted and developed natural immunity. This passive immunity protects the neonate until weaning, and typically lasts until about 16 weeks of age (1,10).

All elements of colostrum are critical to the survival of the newborn; the key difference between colostrum and milk is in the water content and nutrient composition (1). Colostrum contains less water than milk, and is therefore sticky and with a concentrated appearance when compared with milk. The water content will gradually increase from day 1 to day 3 (1,10,11). Additionally, lactose concentrations in colostrum are lower than those in milk, whilst protein and fat levels are higher. Energy content of milk also increases throughout lactation (1,10). It is not until after the first few days of nursing that neonates develop abundant glycogen reserves. This initial lack of glycogen results in the neonate needing to be nursed or fed frequently, sometimes as often as every 2 hours for the first week or so of life.

The second important concern for newborn kittens and puppies is their inability to maintain body temperature. Neonates must be kept in an environment that is 85-90°F/29.4-32.2°C during the first week of life, and 80-85°F/26.7-29.4°C during the second week, as they are unable to thermoregulate (Figure 2). If neonates are unable to stay warm, they risk hypothermia. This can result in difficulties with eating and, if tube fed, problems with digesting food, and a failure to eat may result in rejection by the bitch or queen (1,10-12). The best source of warmth is the mother. After 6 days the neonates are able to shiver, but are still very susceptible to becoming chilled; keeping the environment warm and free of drafts is extremely important during the first few weeks of life.

Orphaned kittens and puppies

Kittens and puppies are typically raised without incident by their dam and weaned to an appropriate growth diet. However, with orphaned neonates, other feeding approaches are required. Neonates are considered ‘orphaned’ if they lack sufficient care from the bitch or queen for survival (11,12). If a nursing queen or bitch is available, it is ideal to try to foster the orphaned offspring with her. Orphaned neonates have the same requirements as neonates that have a mother, i.e., they still need adequate nutrition and warmth. If a foster mother is not available, kittens and puppies can be hand-raised. Very young or debilitated neonates can be raised by tube feeding, or with bottle feeding in older and healthier neonates. The latter is the safer and easier option (Figure 3), but can be time consuming, especially if the size of the litter is larger than expected. With appropriate training from the veterinary team, tube feeding can be effectively mastered by most clients, providing them with a more rapid, albeit slightly riskier, method for delivering nutrition (13).

Milk from cows and goats contains less fat, protein, calcium and calories when compared to milk from queens and bitches, and therefore should be avoided (10,12). Recommendations for feeding vary, but typically range between 13-18 mL/100 g bodyweight (using a formula with a caloric density of approximately 1 kcal/mL) initially, and then gradually increasing as the orphan gains weight (1,10,13). Every feeding episode should be followed with anogenital stimulation using a cotton swab or warm cloth to encourage urination and defecation.

The ratio of casein:whey in the milk also differs between species. Casein is the solid protein in milk, while whey is the liquid protein. The amount of casein may affect protein digestion, mineral utilization and the amino acid composition of the milk. The ratio for cats is 60:40 and 70:30 for dogs (1,10). Importantly, just as bitch’s milk is inadequate for kittens, so too is queen’s milk inadequate for puppies, due to insufficient lactose and calcium levels.

Assessing orphan puppies and kittens

Regular reassessment of any feeding plan should consider the overall health, appearance, activity level, hydration status and weight gain of the orphans. For kittens, the expected weight gain would be ∼15-20 g/day (12), and for puppies 4 g/day/kg of anticipated adult weight (13). Chronic whimpering or vocalization may be an indication of discomfort or hunger, and warrants a reassessment of the feeding plan; low birth weight is correlated with poor survivability. Standard mean birth weights are given in Box 1.

Box 1. Standard mean birth weights for kittens and puppies (3,11,12,14).

In the first 24 hours of life, puppies and kittens may lose a small amount of weight due to slight dehydration and initial defecation (14), but they should then gain daily, doubling their birth weight by 7-10 days of age. Research has shown that puppies that lost >10% of their birth weight within the first 2 days of life were much less likely to survive until weaning as opposed to those that maintained or gained weight in that time (14). Thus, it is important for the healthcare team to weigh all neonates at birth, 12 and 24 hours of life, and then daily, carefully recording the results in order to detect any unexpected changes in body weight (Figure 4).

Milk replacers

When feeding orphans, it is recommended that a commercial milk replacer be used, as many home-prepared recipes are not adequate to meet the needs of a growing puppy and kitten. These have usually been developed through trial and error, and their actual nutrient content is unknown (10-12).

The American Association of Feed Control Officials (AAFCO) does not provide detailed guidelines for testing milk replacers, so careful attention should be paid to a manufacturer’s information on their products in terms of nutrient composition, nutritional integrity and feeding efficacy, as this will help in choosing the best option (1). It is important to remember that even the best milk replacer cannot provide the neonate with the variety of antibodies found in colostrum, so extra care must be taken to maintain a clean environment and prevent transmission of disease (1,10). It is imperative that the feeding materials (e.g., bottles, nipples, tubes) be cleaned and disinfected between feedings. The milk replacer itself should be made fresh or refrigerated between feedings to decrease the incidence of bacterial contamination. It is advisable that only the volume of milk replacer that will be consumed within a 24-hour period should be prepared, and any remaining quantities not used at that feeding stored in the refrigerator (11).

Key nutrients

Water

Water is the most important nutrient in all stages of life; however, hydration status can be difficult to assess in neonatal puppies and kittens. Neonates have less subcutaneous fat, making skin turgor/tenting a rather inaccurate indicator of hydration status. Puppies and kittens with light pigmentation that are well-hydrated typically display a deep pink coloration of the ventrum, muzzle, and oral mucous membranes (Figure 5) (14), whereas dehydration may lead to a darker pink/red color, but this measure is very subjective. Dehydrated neonates may also have dry oral and ocular mucous membranes; however, be cautious when assessing oral mucous membranes in neonates that have recently nursed, as milk on the mucous membranes will make them feel slick, which may be mistaken for normal hydration. Normal urine in neonates is dilute with no discernible color (14), so any yellow coloration is suggestive of dehydration.

Puppies and kittens require a relatively high-water intake. A typical neonatal puppy needs ~130-220 mL/kg bodyweight daily, whilst a neonatal kitten needs ~4.4-6.5 mL per 28g bodyweight (11,12,14). Orphaned puppies and kittens should receive ~180 mL of water/kg bodyweight daily to ensure success in feeding. If necessary, additional water should be given until 180 mL/kg bodyweight is reached if the milk replacer doesn’t provide this at the recommended dilution.

Energy

The milk from a queen or bitch has an energy digestibility of > 95%. This high digestibility maximizes its usage and helps neonates survive the critical first weeks. Bitch’s milk is high in energy and provides about 146 kcal (610 kJ)/100 g GE (gross energy); the average daily energy intake for puppies is about 240 kcal (1 MJ)/kg bodyweight during the first four weeks of life (12).

Kittens less than one week old will take a volume equal to 10-15% of their bodyweight as milk (or properly formulated milk replacer) per day; between weeks 1-4 they will take a daily volume equal to 20-25% of their weight (11).

Protein and amino acids

The protein digestibility of canine milk is very high, with nitrogen retention of ~ 90% during the first week post-partum. Bitch’s milk also contains more than twice as much protein per volume than cow’s milk (7.5% vs. 3.3%). (12), and also contains high levels of arginine, lysine and branched-chain amino acids. When assessing and formulating milk replacers, this nutrient profile needs to be considered, as it also reflects the enormous anabolic activity of puppies at this young age. Protein requirements should be met if a puppy ingests adequate amounts of energy equivalent to that of bitch’s milk.

The minimum protein requirement of nursing kittens has not been established, although it is assumed to be similar to that for weanling kittens, at ~ 18-20% DM (dry matter). The protein content of queen’s milk ranges from 33-44% DM (11). 

It is essential for any milk replacer to have adequate protein and essential amino acid content. The levels of arginine and histidine in the formula are crucial, as a deficiency can result in cataract formation in neonates and may lead to anorexia and impaired growth. Taurine is essential for normal growth and development of kittens; a queen’s milk supplies about 300 mg taurine/L, but cats fed low-taurine foods will have substantially lower levels in their milk, which may impair normal neonate growth and development. Bovine milk is a poor source of taurine, so if an owner uses a homemade formula based on cow’s milk, it is imperative that it is supplemented with taurine (30 mg taurine/100 mL milk replacer). 

Fat

Milk fat is an important source of energy and essential fatty acids for nursing kittens. The make-up of a queen’s diet influences the quality and quantity of milk fat, which then translates into the fat composition of the neonatal kitten. Throughout the lactation period, a queen’s milk will increase in fat content; average fat concentrations are typically 28% DM. The milk also provides the essential fatty acids, linoleic and arachidonic acid at 5.8% and 0.5% DM respectively. Docosahexaenoic acid (DHA) is also essential for normal retinal development and function in kittens, and the DHA concentrations in a queen’s milk will reflect her dietary intake. The recommended DM level of DHA plus eicosapentaenoic acid (EPA) for kittens after weaning is 0.01%, with EPA not exceeding 60% of the total DHA plus EPA. These levels are said to be suitable for neonatal orphan formulas as well.

Bitch’s milk should contain 9 g or more fat/100 g of milk. The bitch’s milk contains a high percentage of unsaturated fatty acids and is rich in linoleic acid. Do remember that milk fat and fatty acid composition are highly variable components of milk, and will often reflect the dietary intake of the bitch. The fatty acid composition of milk may be influenced by the type of dietary fat fed in conjunction with the fatty acid profile of endogenous fat deposits. 

Retinal function of young dogs has been shown to be improve when foods containing long-chain omega-3 (n-3) polyunsaturated fatty acids are fed during gestation and lactation (15). EPA should not exceed 60% of the total amount of DHA plus EPA, subsequently DHA needs to be at least 40% of the total DHA plus EPA, or 0.02%. DHA has also been shown to improve learning in dogs (16). Linoleic acid is required for normal growth, with the linoleic acid content of bitch’s milk being 4.9% DM. 

Carbohydrate

Lactose concentration of a queen’s milk ranges from 14-26% DM, but no requirements for carbohydrates have been established for nursing kittens. It is important that the veterinary team advise owners that overfeeding cow’s milk can lead to diarrhea, bloating and abdominal discomfort in kittens due to bacterial metabolism of undigested lactose in the large intestine. They should therefore be advised to limit the quantities given and to terminate feeding cow’s milk if any intolerance occurs.

Levels of lactose (the primary carbohydrate in milk) in bitch’s milk vary between 3.0-3.5%, which is ~30% lower than in cow’s milk. Lactose should be the main carbohydrate source during the first weeks of a neonate puppy’s life to avoid diarrhea. Pancreatic amylase activity is insignificant at four weeks of age and low at eight weeks, and conversely, intestinal lactase activity is greater until about four months of age.

Calcium and phosphorus

Calcium concentrations are low in feline colostrum (0.22% DM) but then increase to ~ 1% DM by mid to late lactation – as the neonate’s requirements are limited in early life stages and then increase with bone mineralization and growth. Milk phosphorus concentrations do not vary to the same extent. Calcium-phosphorus ratios increase from a low of 0.4:1-0.8:1 on day 1 of lactation to approximately 1:1 between weeks 1 to 3 (11,17).

In bitches, calcium levels are very high in colostrum, but they then decrease to a level lower than that found in mature milk after two to three days. The calcium-phosphorus ratio remains consistent around 1.3:1. Calcium and phosphorus levels in milk are similar among canine breeds.

Conclusion

Nutrition plays a major role in the health and development of growing kittens and puppies, and directly affects the immune system, body composition, growth rate and skeletal development. A neonate’s diet is controllable and is perhaps the most important factor that influences health and disease. It is important for the veterinary team to remember that the goal of a feeding plan for both kittens and puppies is to create a healthy adult, therefore the specific objectives of a proper neonate feeding plan are to achieve healthy growth and optimal development, whilst minimizing risk factors for disease.

References

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