The canine population is characterised by its diversity in terms of age, sex and sexual status, size, breed, physiological status (eg gestation, lactation), activity and health status. Yet, 60 years ago, a single diet was recommended for all dogs, regardless of those factors. Over the years, dietary requirements have become better defined, and diets have been formulated accordingly.
The National Research Council (NRC) is the scientific authority that establishes dietary requirements for domestic species, including birds (NRC, 2006). It relies on panels of academic experts who review the literature and make recommendations. The first NRC guideline for dogs was published in 1953 and for cats in 1986. Several editions followed, the last in 2006.
Most of the data on the nutrient requirements for cats and dogs come from a few Beagle and domestic shorthair cat colonies, and a degree of extrapolation is needed to apply them to the general population. For example, colony dogs and cats are much more active than pets and therefore energy requirements must be adjusted.
Most of the data on the nutrient requirements for cats and dogs come from a few Beagle and domestic shorthair cat colonies, and a degree of extrapolation is needed to apply them to the general population
Refinement of diet formulations has continued, with the aim of meeting the specific needs of different groups of cats and dogs. For example, puppies and kittens clearly have higher energy and nutrient requirements than adults. Moreover, they require smaller-sized kibbles and, during weaning, kibbles that can be easily rehydrated to form a slurry. Puppy and kitten diets are also recommended for gestating and lactating females to fulfil their very high energy and nutrient needs. The side benefit of this is that puppies and kittens naturally eat their mothers’ diets.
Breed size and early life – tailor-made nutrition for optimal growth
Early growth (especially up to six months of age) is a very sensitive period for large-breed dogs. Excessive energy and calcium intake have been shown to promote bone and joint diseases such as hip dysplasia and panosteitis (Nap and Hazewinkel, 1994) due to an excessive rate of growth and the associated excess weight inducing stress on the immature skeleton.
Growth curves are now available to help owners adjust food intake to achieve the optimal growth rate for their pets (Salt et al., 2017, 2022). Owners often believe that a faster growth rate will result in a larger, heavier dog. Nothing could be more wrong: they will just reach their adult size and weight faster on an immature skeleton.
Small dogs are less sensitive to bone and joint ailments but are at risk of obesity if overfed during growth. Growth curves can also help pet owners maintain their pets at an optimal weight.
Age – tailored nutrition for the senior pet
Although the population of older pets is increasing, the 2006 NRC panel of experts concluded that there was not enough evidence to establish a dedicated energy and nutrient dietary guideline for senior cats and dogs (NRC, 2006).
Establishing dietary requirements for senior pets is difficult. One reason for this difficulty is that the senior population is not homogeneous according to age. For example, although most cats start to lose weight by 10 to 12 years of age, their body condition may vary from very lean to overweight. The other issue is that most ageing pets develop chronic diseases that affect their nutritional requirements. Furthermore, the life expectancy of dogs is affected by size; small dogs live longer than large dogs, and giant dogs, especially Great Danes, have a much shorter lifespan.
Because of this lack of guidance, current senior diets fulfil “adult” dog and cat dietary requirements; however, their formulas are adjusted to maintain optimal weight and provide support for age-related problems. These include osteoarthritis, for which chondroitin sulfate, glucosamine and omega-3 fatty acids (eicosapentaenoic and docosahexaenoic acids) can be beneficial. Other nutritional formulas can help to slow the progression of sub-clinical renal disease (a reduced phosphorus content), cardiac disease (taurine and carnitine) and cognitive decline (inclusion of antioxidants, docosahexaenoic acid and medium-chain triglycerides) (Geddes et al., 2016).
The size and hardness of kibbles are also considered in diet formulations for ageing pets. Wet food is encouraged, and palatability factors are increased to compensate for the loss of smell and taste.
Size – is tailor-made nutrition breed-specific?
As mentioned, the canine population shows a large variation in size, ranging from the 1kg Chihuahua to the 100kg Mastiff.
When fed the same diet, large dogs tend to have softer and moister faeces than small dogs. This has been the topic of four successive PhD theses at the Veterinary School of Nantes (Oniris, France), summarised in a review paper (Weber et al., 2017). Briefly: large dogs have a larger colon, their colonic transit time is longer and their colonic fermentation activities and permeability are higher than small dogs, all of which explain the moister and softer faeces.
But what are the implications of these observations? Nutrients not digested in the small intestine will induce more colonic fermentation in large dogs than in small dogs. Large dogs will thus be more sensitive to high levels of protein (especially those of lower digestibility), poorly cooked starches and excessive levels of fermentable fibres. As a result, a diet formulated with a higher level of non-fermentable fibre and/or a lower level of fermentable fibre will improve the faecal quality of a large dog but will tend to produce hard, dry faeces when fed to a small dog.
Diet formulas will take into account the combination of all these differences to meet energy and nutrient requirements and at the same time use ingredients and kibble characteristics that may modulate disease predispositions
Together, these observations and the different dietary sensitivities of different-sized breeds support formulations based on size as well as age. Large dogs have a greater risk of bone and joint diseases during growth than small dogs. Osteoarthrosis occurs more commonly and at an earlier age in large dogs than small ones. In contrast, small dogs more commonly develop periodontitis and urinary stones. In terms of cardiac conditions, small dogs tend to suffer from mitral valve diseases and large dogs from dilated cardiomyopathy. Small dogs live longer than large ones. Diet formulas will take into account the combination of all these differences to meet energy and nutrient requirements and at the same time use ingredients and kibble characteristics that may modulate disease predispositions.
How do breed disease predispositions affect tailor-made nutrition?
In addition to the effect of size, particular dog breeds are associated with conditions modifiable by nutrition. For example, Cocker Spaniels, Cavalier King Charles Spaniels, Labradors, Golden Retrievers and many others are at increased risk of obesity. German Shepherds and Rottweilers commonly develop gastrointestinal ailments and have softer faeces.
Diets can therefore be tailored for specific breeds as well as for dog size, optimising energy and nutrient levels while incorporating nutrients and ingredients with targeted health benefits.
The effect of neutering on nutrition for cats and dogs
It has long been known that pets gain significant amounts of weight following neutering (Nguyen et al., 2004). A survey at the end of the 1990s indicated that most veterinarians either did not make any recommendations on feeding after neutering or advised a reduction in the amount of food. This is not particularly helpful or easy advice for pet owners to follow, especially if they have a cat fed by free choice. Another group of veterinarians recommended a urinary diet; at the time, those diets were very high in fat and energy and could induce a 1kg weight gain within two months. Finally, a minority of veterinarians recommended a weight maintenance diet.
There is no recent survey, but this might still be an issue today. These examples highlight the importance of having diets specifically formulated for neutered pets and providing veterinarians and owners with appropriate guidelines. The transition to a diet tailored for neutered pets must occur just after neutering surgery because the appetite of such a pet increases within 48 hours.
Beyond nutritional factors – enrichment, therapeutics and learning
For many years, kibbles were considered only as a means of delivering nutrition. We now realise that kibbles have other important functions. They promote chewing, thereby allowing the release of factors that help reduce tartar and gingivitis (Hennet et al., 2007). Chewing also slows down food intake and promotes satiety. The shape of the kibble also affects energy density and food volume, which can be used to help owners provide the right amount of food for their pets. Furthermore, the rehydration potential of kibbles to make a slurry is of interest for feeding junior and senior dogs.
For many years, kibbles were considered only as a means of delivering nutrition. We now realise that kibbles have other important functions
The importance of therapeutic diets in the prevention, management and resolution of various pathologies has become well established. Until recently, however, each therapeutic diet targeted just one condition, but mixing diets is not an option for dogs that suffer from several conditions at the same time. Now, there are diets on the market that are indicated for the most common disease combinations: obesity and osteoarthritis, for example.
The patient at the core of tailor-made nutrition
The next level of tailoring is to consider all the physiological and pathological characteristics of a patient and formulate a dedicated diet for that individual. This service has been available for the last few decades from boarded veterinary nutritionists who formulate individualised homemade diets. Unfortunately, veterinary nutritionists are scarce, and not all pet parents are willing to cook for their pets. Recently, another option has been proposed. This entails the veterinarian entering the patient’s information into an application, upon which an algorithm calculates the optimal combination of a set of kibbles to match the energy and nutrient requirements of that individual patient.
Researchers around the world are working to determine the best diets for humans according to their genome, metabolomes (levels of metabolites in physiological fluids) and microbiomes (Ogunrinola et al., 2020; Zeisel et al., 2013). Most of this research is on laboratory animals, and little work has been done on pets. These endeavours are proving to be much more complex than expected, and the science is still in the early stages of development.
Conclusion
There are many individual factors upon which diets can be tailored to best fulfil the needs of a dog or cat. Over the past 60 years, we have progressed from a single diet for all dogs to diets that take into account the life stage, sexual status, size, breed and therapeutic needs of the pet. Nutrigenomics, metabolomics and a better understanding of the microbiome will allow us to make further advances, but those sciences are still in their infancy. Diets are already available with formulations for individual patients with complex issues. But there is one consideration that all tailored diets have in common: they can only benefit a dog or cat if they are eaten!
