When counselling pet owners on the care of their new puppy or kitten, there is a plethora of information veterinarians must cover. Among the key education topics is, of course, nutrition, as this is a significant contributor to the healthy growth and development of a young animal. Too often, however, veterinary teams experience pain points facilitating these conversations, stemming from misconceptions surrounding appropriate feeding methods, a lack of familiarity with the nutrients required for pets’ growth, and how energy needs change during growth.
To encourage the best outcomes for our patients, it is important to understand:
- the nutritional requirements of different growth phases;
- differences between adequate and optimal nutrition; and
- how to effectively feed a young animal.
Additionally, knowing what does and does not define a growth diet can have a significant impact on the nutrition we recommend, along with the future health of our patients.
Nutrition for growth
Both puppies and kittens undergo a rapid growth phase characterized by high-energy needs and nutrient requirements. This is followed by a slower growth phase, which sees a flattening of the curve accompanied by a reduction in energy needs, but with maintained nutrient requirements. The latter phase begins once approximately 80 per cent of adult weight is attained, so the age at which this occurs varies by species and breed.
There are several nutritional factors to consider during each phase. At weaning, a puppy or kitten’s body weight is low and, conversely, their growth rate is high. At this time, about half of the pet’s energy needs go to maintenance and the other half contribute to growth.1 During this period, both nutrient requirements and energy needs are high.
As growth rate eases, energy needs decrease accordingly, moving toward adult maintenance levels, but nutrient requirements in this stage remain high. In kittens, spaying or neutering will decrease energy needs, regardless of the age at which the procedure is performed.2 To account for this, it has been suggested to reduce caloric intake in neutered kittens by 20 to 30 per cent;3 however, it is important to recognize we cannot restrict calories without also restricting nutrients (except in specifically designed formulas which are usually indicated for weight loss and not appropriate for growing animals). As such, it is recommended to stay within the feeding guidelines provided by the manufacturer of the growth diet being fed and to use a diet with a lower caloric density, whenever possible. To avoid obesity, the patient’s growth should be closely monitored via a validated growth curve. Additionally, food dose should be measured using a gram scale.
In dogs, the impact of neutering on energy needs is less clear. While it has been suggested neutered dogs are more likely to be overweight, some studies show neuter status has less of an effect on growth trajectory as compared to other variables across individual animals.4
Photos courtesy Royal Canin Canada
It was once thought feeding a puppy formula to a large- or giant-breed puppy would cause the animal to grow too quickly, which could contribute to orthopedic disease. For this reason, some would recommend an early transition to adult food, as they believed this to be lower in energy and, thus, safer to feed. This practice should be avoided, as it is based on the erroneous assumption that growth diets are higher in calories. In actuality, there is a large range of caloric density in formulas for various life stages and significant overlap in the calorie density of commercial formulas for both adults and puppies. Further, nutrients in adult-dog food formulas are not optimized for growth.
If a diet change is required based on calories, one should avoid going to an adult formula and, instead, select a different growth formula with a lower caloric density.
Macronutrients and micronutrients
Protein needs are highest at the time of weaning and progressively decrease as the growth rate slows. When considering protein, in addition to the total level of protein, both digestibility and specific amino acid profiles should be considered.1
Essential fatty acids, including omega-3 and -6 fatty acids, must be provided in the diet. In particular, the omega-3 fatty acid DHA (i.e. docosahexaenoic acid) is important for sensory and neural development,5,6 and the most rapid development for these systems is within the first six weeks of life. There is a minimum requirement for both DHA and EPA (i.e. eicosapentaenoic acid) for growth, though levels can be optimized.
Growing animals in particular require a highly digestible diet and the choice of carbohydrate is influenced by the physiologic state in these growth phases. The ability to digest various carbohydrates develops at different times in puppies and kittens, and the activity of some enzymes only starts to increase after weaning. In dogs, for example, pancreatic amylase activity for starch digestion doubles between its level at nine to 16 weeks of age and its level at adult age. Additionally, in kittens, lactose digestion decreases rapidly from three to six weeks, while amylase activity increases.1,7,8
While many minerals are important in development, few get as much attention as calcium and phosphorus. Puppies and kittens need more of these minerals than adult dogs and cats in general, but the requirement is still relatively low.
Some may make the error of adding supplements to an otherwise balanced diet without realizing calcium homeostasis is less precise than in the adult and intestinal absorption is not fully regulated before six months of age. This can lead to calcium retention and contribute to developmental bone disease, particularly in large- and giant-breed puppies. The ratio of calcium to phosphorus is critical in puppies, though kittens are less sensitive in this regard.1
An older study exploring the effects of calcium over-supplementation in Great Dane puppies demonstrates this point. Findings showed puppies eating a diet with controlled calcium had normal, uniform bone growth, while littermates consuming a diet with higher calcium demonstrated significant angular limb deformities.9
Although the minimum required levels of calcium and phosphorus are higher for growth diets, one should not assume adult diets are inherently lower in these minerals than growth diets. In fact, the required levels of calcium and phosphorus for growth are within a more precise range than for adults.10
While it is rare for commercial diets to have deficiencies or excesses of other nutrients with important roles such as zinc, iodine, manganese, or vitamin D, A, or C, this can occur more often in homemade or unbalanced diets.1
The microbiome
The microbiome is a burgeoning area of study in veterinary medicine and plays an important role in overall health. Predictably, this is also true for our youngest patients, as the development of the intestinal microbiome begins early and can influence a host of factors with effects on physiology, immunity, and behaviour.
The microbiota utilizes undigested fibre, breaking it down and producing beneficial metabolites, such as vitamins and short-chain fatty acids, which are the primary energy source for enterocytes.11 While fibre is not considered an essential nutrient, prebiotic fibres, such as fructo-oligosaccharides, alongside other prebiotics, such as mannan-oligosaccharides and beta glucans from hydrolyzed yeast, can help nurture the maturing microbiota and have a marked effect on gastrointestinal health.11
The microbiome has an impact on immunity at the level of the gut. It is important to be mindful that fostering the development of a thriving gut microbiome is a key nutritional goal beginning early in life. While the microbial ecosystem of immature puppies and kittens is more diverse than that which is seen in adult pets, it is less stable and takes longer to adapt to change. This is why the frequency of diet changes should be minimized during the puppy and kitten stage of life.12 If a diet change is required, this would, ideally, occur as a slow transition while monitoring stool quality to adjust the rate of diet transition as required.
How to feed
Obesity has become a significant problem in pet populations, and prevention is preferred to treatment. Excess energy intake, weight gain, and subsequent obesity can contribute to developmental orthopedic disease, and places a pet at increased risk for developing future complications from metabolic conditions. As such, maintenance of a healthy body weight should begin at the start of life.
This necessity should be emphasized throughout the growth period. It is during this phase when new fat cells are created, which can lead to hyperplastic obesity, as opposed to obesity in adulthood where existing fat cells grow (i.e. hypertrophic obesity). By comparison, hyperplastic obesity carries a worse prognosis, as the number of fat cells that can grow will be greater in an adult pet that was obese as a puppy or kitten.
Growth should be tracked using validated growth curves. Understanding how to interpret the curve can help determine if body weight is increasing too quickly and if a pet is at risk for obesity (conversely, if growth is slower than expected, this may signal an underlying disease condition or nutritional issue). More frequent weigh-ins will help in the interpretation of the growth curve and afford the opportunity to adjust food dose as necessary, particularly when the slow-growth phase begins. The use of a gram scale, which can be used with dry or canned formulations, is strongly recommended to ensure accurate portions are being fed.13
Meal feeding should continue throughout the growth period. The frequency of meals can be adjusted based on growth phase and breed size—large-breed dogs, for example, are more susceptible to soft stool and diarrhea,8 and feeding of smaller portions more frequently introduces a smaller volume of food for fermentation at any given meal. Three or more meals per day during the rapid-growth phase and two or more per day in the slow-growth phase are recommended.
‘Required’ versus ‘optimal’
When it comes to the formulation of diets for pets, there are surprisingly few regulations. Available guidelines include only minimum or maximum values, and may exclude nutrients which, while not considered essential, are beneficial.
Young puppies and kittens have an immature immune system and experience what is referred to as the immunity gap between four and 12 weeks of age. During this time, the protection they received from colostrum is declining while their own immune system is still developing. Several nutrients can be used to support immune system development during this vulnerable period. Among these are antioxidants, such as vitamin C, vitamin E, lutein, and taurine, and beta-carotene, which helps stabilize free radicals and support the cells involved in the immune response. Additionally, beta-glucans, which come from yeast cell walls, help activate the immune cells in the gastrointestinal tract, where many pathogens are first encountered.1,14,15,16
It is important that the diet of a puppy or kitten is highly digestible—and pet owners may appreciate the resulting well-formed, easy-to-clean-up stool. Several factors can affect digestibility, including choice of ingredients, grinding of raw materials, cooking of the food, the fibre balance, and even the shape of a kibble (a greater surface area provides more opportunity for digestive enzymes to make contact and can encourage an animal to bite or chew more if they are prone to swallowing their food whole).
Though we have already discussed fibre in the context of the microbiome, this can have many benefits in a growing pet. For example, large-breed puppies, with their greater susceptibility to soft stool, may benefit from a diet containing a higher proportion of non-fermentable fibre. Additionally, fibre has a satietogenic effect, helping pets to feel full while consuming fewer calories, which can have implications for obesity prevention.
Closing thoughts
Few interventions for puppies and kittens have the same level of impact as optimized nutrition and feeding practices. After all, the nutrition we provide our puppy and kitten patients influences their developing immune systems, neural and sensory function, bone growth, and virtually every other body system.
By staying mindful of a patient’s evolving energy needs and employing the use of both a weigh scale and growth curves, we can prevent obesity before it happens. It seems likely the full importance of the microbiome has yet to be discovered and nurturing a thriving microbiota may lead to a myriad of positive outcomes. With every puppy and kitten in our practice, we should strive to provide nutrition which not only meets the requirements for growth, but helps set up our patients for a lifetime of good health.
James Wenzel, DVM, BSc., is a conveyor of scientific conversations, embracer of evidence-based interventions, and is replete with nutrition know-how as it pertains to the dog and cat. A graduate of the Ontario Veterinary College, Dr. Wenzel has served as a scientific communications specialist with Royal Canin since 2017 and has counselled hundreds of pet owners, students, and professional colleagues about the best ways to approach the age-old question of, “What do I feed my pet?”
References
1 Hand et al. 2010. Small Animal Clinical Nutrition 5th edition. Mark Morris Institute, Topeka, Kansas
2 Alexander LG, Salt C, Thomas G, Butterwick R. 2011. Effects of neutering on food intake, body weight and body composition in growing female kittens. Br J Nutr; 106:S19-S23. https://pubmed.ncbi.nlm.nih.gov/22005425
3 Belsito KR, Vester BM, Keel T, Graves TK, Swanson KS. 2009. Impact of ovariohysterectomy and food intake on body composition, physical activity, and adipose gene expression in cats. Journal of Animal Science; 87: 594-602. https://pubmed.ncbi.nlm.nih.gov/18997063/
4 Lefebvre, SL, Yang, M, Wang, M, Elliott, DA, Buff, PR, Lund, EM. 2013. Effect of age at gonadectomy on the probability of dogs becoming overweight. J. Am. Vet. Med. Assoc; 243, 236-243. https://pubmed.ncbi.nlm.nih.gov/23822081/
5 Heinemann KM, Bauer JE. 2006. Docosahexaenoic acid and neurologic development in animals. J. Am. Vet. Med. Assoc; 228(5):700-705. https://pubmed.ncbi.nlm.nih.gov/16506930
6 Zicker SC, Jewell DE, Yamka RM, Milgram NW. 2012. Evaluation of cognitive learning, memory, psychomotor, immunologic, and retinal functions in healthy puppies fed foods fortified with docosahexaenoic acid-rich fish oil from 8 to 52 weeks of age. JAVMA; 241(5):583-594. https://pubmed.ncbi.nlm.nih.gov/16506930
7 Harper EJ, Turner CL. 2000. Age-related changes in apparent digestibility in growing kittens. Reprod Nutr Dev; May-Jun 40(3):249-60. https://pubmed.ncbi.nlm.nih.gov/10943604
8 Weber M, Martin L, Biourge V, Nguyen P, Dumon H. 2003. Influence of age and body size on the digestibility of a dry expanded diet in dogs. J Anim Physiol Anim Nutr (Berl). Feb; 87(1-2):21-31. https://pubmed.ncbi.nlm.nih.gov/14511146/
9 Hazewinkel et al. 1985. Radioimmunoassay for canine calcitonin. Influences of different calcium intakes on calcium metabolism and skeletal development in young Great Danes. [Thesis]. [Netherlands]. Utrecht University. p33. https://pubmed.ncbi.nlm.nih.gov/3810633/
10 AAFCO Official Publication. 2022. 1800 S. Oak Street, Suite 100, Champaign, Ill.
11 Barko,PC, McMichael MA, Swanson KS, Williams DA. 2017. The gastrointestinal microbiome: A review. J Vet Intern Med; 32(1):9-25. https://pubmed.ncbi.nlm.nih.gov/29171095/
12 Guard BC, Mila H, Steiner JM, Mariani C, Suchodolski JS, et al. 2017. Characterization of the fecal microbiome during neonatal and early pediatric development in puppies. PLOS ONE; 12(4): e0175718. https://pubmed.ncbi.nlm.nih.gov/28448583/
13 Coe JB, Rankovic A, Edwards TR, Parr JM. 2019. Dog owner’s accuracy measuring different volumes of dry dog food using three different measuring devices. Vet Rec; 185(19):599. https://pubmed.ncbi.nlm.nih.gov/31409751/
14 Kim, HW, BP Chew, TS Wong, JS Park, BB Weng, KM Byrne, MG Hayek, GA Reinhart. Modulation of Humoral and Cell-mediated Immune Responses by Dietary Lutein in Cats. 2000. Veterinary Immunology and Immunopathology 73 (3-4) (March 15): 331-41. https://pubmed.ncbi.nlm.nih.gov/10713345/
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