We all know the old adage that children and teenagers can eat you out of house and home because it is a critical stage of rapid growth and development in their life. The growth stage from weaning to adulthood for puppies and kittens is equally important, so it is imperative that we understand how to feed them properly to promote healthy growth and development. Ultimately, the goal for puppy and kitten nutrition is to ensure that they develop into healthy adults.
Energy and nutrient requirements for growth
One of the main reasons this stage of development is so calorically demanding is that puppies and kittens must consume enough energy to not only maintain their current body condition and functions but also support growth into their eventual adult size and condition. Thus, it is not surprising their energy requirement (calculated in kcals) can be more than double that of a healthy adult animal of equivalent size.
Puppies and kittens must consume enough energy to not only maintain their current body condition and functions but also support growth
Growth should occur at the proper rate – we are aiming for the “Goldilocks” zone of growth that is not too rapid and not too slow – to maintain a body condition score between 4 and 5 out of 9 (Figures 1 and 2). Overly rapid growth can potentially lead to skeletal abnormalities and developmental orthopaedic disease, particularly in large-breed dogs (Hedhammer et al., 1974; Lavelle, 1989; Kealy et al., 1992). In addition to encouraging overly rapid growth, excess dietary energy can lead to obesity. At the other end of the spectrum, underfeeding during this critical developmental phase can limit overall growth such that the individual may not reach their full growth potential.
The six classes of nutrients are water, protein, fat, carbohydrates, vitamins and minerals. Protein, fat and carbohydrates provide energy for growth. Meanwhile, vitamins, minerals and water do not provide energy but are also nutrients required for healthy growth. Some of these critical nutrients are briefly discussed below.
Protein
Protein requirements for puppies and kittens are higher than that of adults to support their growth. It is important to note that higher levels of protein in the diet have not been shown to negatively affect skeletal development during growth of giant-breed dogs when fed calorically appropriate diets (Nap et al., 1991).
Fat
Fat is not only a source of concentrated energy for growing animals, it is also a critical source of essential fatty acids and a carrier for fat-soluble vitamins. Essential fatty acids contribute to the neurological and retinal development of puppies and kittens. In fact, several studies looking at increasing the levels of the omega-3 fatty acid docosahexaenoic acid (DHA) in the diet of puppies showed those fed DHA-enriched diets significantly outperformed low-DHA puppies in tests of neurological development, including trainability and long-term memory (Kelley et al., 2004; Kelley, 2008; Zicker et al., 2012).
Vitamins and minerals
Vitamins and minerals are also very important during growth. Having the right balance and amount of minerals is especially critical. While puppies require more calcium, phosphorus and other minerals than adult dogs, it is essential these nutrients are supplied in the proper amounts and proportions.
An increased risk of skeletal deformities occurs if there is excessive or deficient calcium intake, or if the calcium to phosphorus ratio is reversed
An increased risk of skeletal deformities occurs if there is excessive or deficient calcium intake, or if the calcium to phosphorus ratio is reversed. The recommended ratio of calcium to phosphorus is between 1:1 and 2:1 for small- and medium-breed puppies (AAFCO, 2022) and between 1:1 and 1.5:1 for large- and giant-breed puppies (Hazewinkel et al., 1987, 1991). For kittens, AAFCO guidelines (2022) recommend a minimum of 1 percent calcium and 0.8 percent phosphorus on a dry matter basis.
| For more in-depth information on these critical nutrients, please see Dr Sherry Lynn Sanderson’s overview of small animal nutrition (2016). |
Calculating energy requirements
Now that we understand the basic energy and nutrient requirements for the optimum growth of puppies and kittens, how do we calculate an individual animal’s energy needs?
The standard method for calculating energy requirements is to start by determining the “resting energy requirement” (RER) with this calculation: RER = 70 x (body weight in kg)0.75. This calculation can easily be done with the calculator on your phone – just turn it sideways and use the “xy” key to do the exponential calculation. However, with puppies and kittens, you want to use their current body weight, not their expected adult weight.
The next step is to calculate the puppy/kitten’s “maintenance energy requirement” (MER), which is the RER multiplied by an MER factor. Use Table 1 to determine the appropriate MER factor to use. Looking at the MER factors, you will notice the high energy demands of growth compared to adults and the reduced energy demands that occur due to neutering. You can also see that the length of the growth period also depends on the adult size of the individual.
| Life stage | Dog MER factor | Cat MER factor |
| Growth (puppy, weaning to 4 months) | 3 | |
| Growth (puppy with adult weight under 25kg, 5 to 12 months) | 2 | |
| Growth (puppy with adult weight over 25kg, 5 to 12+ months) | 2 | |
| Growth (kitten, weaning to 4 months) | 2 | |
| Growth (kitten, 5 to 6 months) | 2.5 | |
| Growth (kitten, 7 to 10 months) | 2 | |
| Adult maintenance (intact animal) | 1.8 | 1.4 |
| Adult maintenance (young adult, spayed/castrated) | 1.6 | 1.2 |
| Adult maintenance (obese prone or senior, spayed/castrated) | 1.4 | 1 |
| Adult weight loss (use ideal weight calculation rather than current body weight) | 1 | 0.8 |
| Adult weight gain (use ideal weight calculation rather than current body weight) | 1.4 to 1.6 | 1.2 to 1.4 |
| Critical illness (current or ideal body weight) | 1 | 1 |
Example calculation
In the case of a 20-week-old male Labrador Retriever puppy who is 15kg with a BCS of 5/9 and an expected adult weight of approximately 30kg, we would select the MER factor of 2 (Table 1). The energy calculations would be as follows:
- RER = 70 x (BW in kg)0.75 = 70 x (15kg)0.75 = 533kcal/day
- MER = RER x (MER factor) = 533kcal x 2.0 = 1,066kcal/day
Therefore, this puppy would require approximately 1,066kcal/day of energy. If he was being fed puppy food that contains 305kcal/cup, he should be fed approximately 3.5 cups of food to meet his current energy requirements.
One size fits all?
Keep in mind that these energy calculations are estimates of the animal’s energy needs – very good ones, but still estimates. Each individual animal’s energy requirements will vary depending on factors like their particular breed/size, activity level and life stage. Additionally, as puppies and kittens grow, their energy requirements often change, even from week to week in some cases. This can make it a bit more difficult to track the appropriate amount of food to be fed, and is why we need to instruct pet owners in how to monitor body condition and weight during the growth phase so they can adjust the feeding regime appropriately. They need to bear in mind that the energy needs of puppies and kittens increase as they grow and plateau as they mature.
We need to instruct pet owners in how to monitor body condition and weight during the growth phase so they can adjust the feeding regime appropriately
One easy way to monitor the growth of puppies and kittens is to use puppy growth charts (Figure 3). These charts were scientifically developed in a similar manner to those used to monitor children’s growth and are valid for dogs (up to a predicted adult weight of 40kg) and cats. Growth charts can be used to promote healthy growth and help avoid weight problems in the future. By regularly plotting a puppy or kitten’s weight on the corresponding chart, the pet owner and veterinary team can be alerted to potential problematic growth early, thus allowing for greater opportunity to correct the issue by altering food intake or exploring any possible underlying growth disorders.
Impact of neutering on energy requirements
Spaying or castrating alters a pet’s energy requirements, which can ultimately impact a pet’s weight. Studies have shown that neutered cats will increase their food intake, and thus their weight, within just a few days of their spay or castrate surgery (Fettman et al., 1997; Kanchuk et al., 2003; Nguyen et al., 2004).
It is important to educate owners about the propensity for weight gain after a spay or castrate, discuss the health risks of obesity and encourage them to adjust the amount fed
The procedure is typically performed between 6 and 12 months of age when energy requirements start to plateau or even decrease as the pet’s growth rate slows. Additionally, their physical activity can decrease with age and neuter status, further altering their energy requirements. Therefore, it is important to educate owners about the propensity for weight gain after a spay or castrate, discuss the health risks of obesity and encourage them to adjust the amount fed to maintain their pet’s ideal body condition.
Transitioning to adult diets
Puppies and kittens should be fed a diet appropriate for growth until the end of the growth period and then transitioned to an adult diet that meets their individual nutritional needs. Different sized dogs enter and leave life stages at different ages, thus five different size categories for dogs are delineated (Table 2).
Puppies and kittens should be fed a diet appropriate for growth until the end of the growth period and then transitioned to an adult diet that meets their individual nutritional needs
Dogs complete the growth stage as early as 10 months of age for extra-small and small breeds; however, it can take up to 24 months for giant breeds to reach their adult body size. As there is variation in recommended nutrients for different sizes of dogs, it is also recommended that size-appropriate puppy food be fed to support healthy growth through this stage.
There is much less size variation for cats so there is a general developmental timeline for most, except for the Maine Coon which can be significantly larger than a typical cat. Most cats complete the growth phase at approximately 12 months of age, while the larger Maine Coon can continue growing until about 15 months old.
| Category | Weight | Growth | Adult | Mature | Ageing |
| Cat | Under 15lbs | Until 12 months | Until 7 years | 7 to 10 years | 10+ years |
| Maine Coon Cat | 11 to 25lbs | Until 15 months | Until 7 years | 7 to 10 years | 10+ years |
| X-small dog | Under 8lbs | Until 10 months | Until 8 years | 8 to 12 years | 12+ years |
| Small dog | 9 to 22lbs | Until 10 months | Until 8 years | 8 to 12 years | 12+ years |
| Medium dog | 23 to 55lbs | Until 12 months | Until 7 years | 7 to 10 years | 10+ years |
| Large dog | 56 to 99lbs | Until 15 months | Until 5 years | 5 to 8 years | 8+ years |
| Giant dog | Over 100lbs | Until 18 to 24 months | Until 5 years | 5 to 8 years | 8+ years |
Conclusion
Over the years, we have learned a lot about the unique nutrient and energy requirements for optimum growth in puppies and kittens. As there are several excellent diets available to support healthy growth and development, it is important the veterinary community helps guide pet owners in making the right food choices for the lifelong health of their pets. Monitoring growth through weight tracking and adjusting food portions as appropriate is quite easy and can help limit the risk of excessive weight gain and obesity-related disease risks later in life.
