Role of proteins: Proteins perform numerous functions in the body, encompassing roles as diverse as structural components of practically all body tissues, enzymes for digestion of food and metabolic reactions, homeostatic hormones and transport proteins, and immunoglobulins and other components of the immune system. Body proteins are constantly being turned over, requiring a supply of amino acid building blocks.
Proteins: Dogs and cats are able to synthesise 12 of the 22 different amino acids found in proteins, but only as long as sufficient nitrogen is present in the diet. These are the so-called non-essential or dispensable amino acids. The other 10 amino acids – the essential or indispensable – must be supplied in the diet and include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Cats require an eleventh amino acid, namely taurine.
Dietary protein and amino acid requirements vary according to life stage and lifestyle, as well as factors such as disease, environmental temperature and stress. The ability of a food to meet these requirements depends upon how digestible the protein is and how well its amino acid profile meets the amino acid needs of body tissues. The latter represents the biological value or quality of a protein.
Protein dietary requirements: National Research Council 2006 recommends that adult dogs should be fed a diet containing at least 25 g protein per 1000 kcal. This requirement increases to 50 g/1000 kcal in female dogs during pregnancy and lactation and 56g/1000 kcal in puppies. Protein requirements are also higher in working and racing dogs, reflecting the demands of increased muscle turnover and protein synthesis.
Protein supplied in excess of requirements is simply converted to energy and stored or utilised as such. There are no recommended maximum protein intakes for dogs.
Myth busted: Anecdotally there are claims that raw meat (high protein) diets are linked with aggression in dogs. This has led to speculation that a high protein level in dog food causes aggression. Brain biochemistry indicates that certain amino acids are linked with production of ‘calming’ hormones; hence there is a leap of faith suggesting that certain diets are calming and others have the opposite effect. Likewise there has been speculation that high protein diets cause kidney disease, especially in cats. This has partly come about because low protein diets are used to treat the symptoms of kidney disease.
Dogs are semi-carnivores, cats are carnivores; this means that they evolved to eat diets rich in protein. For example, the maternal milk of dogs is much higher in protein than human or cow’s milk.
Scientific studies have shown that there is no link between high protein diets and aggression in dogs. Our resident dogs at our Pet Centres in Waltham and Verden, Germany are continuously looked after and monitored with respect to their health, happiness and behaviour. Over many years of feeding foods containing a range of protein levels, we have never experienced any indication of a relationship between dietary protein and aggression.
Similarly, several scientific studies have shown that there is no link between high protein diets and risk of kidney disease in healthy cats and dogs.
The independent international nutrition guidelines for dogs (NRC) are based on the latest science and they have not specified a limit to upper levels of protein for dogs.