243 Award Talk: Ecological factors influencing dog and cat biology.

Abstract The fundamental basis of formulating nutritionally complete foods lays in important studies that determined minimal requirements of nutrients and maximal levels of dietary constituents to prevent toxicities. These studies have also contributed to our current understanding of the digestive physiology and metabolism of both dogs and cats. These studies also revealed that dogs and cats have similarities but also differences. Cats show various so-called “metabolic idiosyncrasies” which are thought to be typical for carnivores. Dogs, however, do not or to a lesser extent show the idiosyncrasies and have some traits more similar to omnivores (e.g. humans, pigs, rats). Dogs have, therefore, been labelled by some as omnivorous in nature. Indeed, carnivorous wolves entered a new food niche created by early agriculturists in the Neolithic Era that was starch-rich and over time left signatures of adaptation in their genome. There were, however, no genetic adaptations that explained the machinery, i.e. enzymes in metabolic pathways, for other ‘omnivorous’ traits. A new ecological context was coined explaining the origin of these traits in dogs being the ‘feast-or-famine’ lifestyle of carnivorous wolves. As with omnivores and herbivores, it is not only relevant to consider what food is eaten, but also when food is available. A lifestyle with large seasonal variations in food availability requires physiological and metabolic flexibilities. A capacity to down-regulate amino acid catabolism, for example, is highly functional to overcome periods of famine and underlies the lower requirements for amino acids in dogs relative to cats. Such flexibilities also allowed dogs to opportunistically enter and thrive in the new food niche, one less rich in protein. Considering dogs as carnivores, and not omnivores by nature, can help to better understand their biology. For both dogs and cats we are actually still learning about what is their ‘normal’ biology. For example, only few studies evaluated the nutritional properties of mice, a typical prey animal in the wild for cats. How do dogs and cats eat, digest, ferment and metabolize when fed prey and what is the impact on their functioning? Answers to such basic research questions will increase our knowledge of dog and cat biology but will help us to understand how their functioning deviates from the situation when they are fed current dry and wet foods. Whether deviations matter for the health and longevity of dogs and cats requires attention, as the goal for life of animals in the wild is reproductive success and not longevity. Considering the ecological history of dogs and cats can provide new insights that we can apply to further optimize their nutrition for health and longevity.