nutritional requirements
All species of felids have unique nutritional requirements within their diet. Felids appear to have no dietary requirement for carbohydrate (Morris et al, 1977) and their bodies utilize other nutrients for energy. Due to a lack of research on specific lion requirements, the nutritional requirements are modeled on those of the domestic cat, which have an approximately equal digestible intake per kg/BW (Allen et al, 1995).
Protein
Felid species require substantially more protein in their diet compared with omnivores such as rats or pigs (MacDonald et al, 1984). Protein is not only used for growth but for maintenance, where carbohydrates would normally be the prime energy source. Felids have a high activity of nitrogen catabolic enzymes in the liver, which have shown to be non adaptive (Rogers et al, 1977). Therefore a low protein diet results in required nitrogen being lost from the body as urea. (Rogers et al, 1977). Estimates for felid protein requirement, once all amino acid requirements are met, range from 12% (Burger et al, 1981) to 16% (Anderson et al, 1980) of the dietary calories, in order to meet the necessary nitrogen levels.
In addition to the essential amino acids needed by most animals, felids have a fundamental dietary requirement for arginine (Morris and Rogers, 1978). A deficiency causes a dramatic response leading to severe hyperammonemia and symptoms of ammonia intoxication (Morris and Rogers, 1978). Arginine is synthesized from citrulline in the kidneys. Activities of two intestinal enzymes have found to be lower in cats; pyrroline 5-carboxylate and ornithine aminotransferase (OAT) required for the synthesis of ornithine and citrulline from glutamate (Morris, 2002) therefore impacting the overall production of arginine.
Felids have a considerably higher dietary requirement for sulphur amino acids than most other mammals, which has been related to their thick hair and need to synthesize felinine in the urine. Taurine is a β-amino sulfonic acid that is present freely in animal tissues. Cats require taurine as a conjugate in for bile salts, but are inefficient at synthesizing it from methionine and cysteine in the liver (Hedberg et al, 2007), therefore it must be consumed within their diet. Studies and observations have shown that a dietary deficiency of dietary taurine is likely to lead to Central Retinal Degeneration (CRD) within felid species. In addition, taurine deficiency can impair reproduction and cause developmental defects (MacDonald et al, 1984)
Lipids
Lipids have three main functions in felids. They provide a concentrated source of energy, essential fatty acids and are a carrier for fat-soluble vitamins (Macdonald et al, 1984). Felids are able digest and utilize high levels of dietary fat (MacDonald et al, 1984)
Most mammal essential fatty acid (EFA) requirements can be met by linoleate, which, through alternating desaturation and elongation, is converted to arachdionate in the liver. Rivers et al (1975) suggested that this system might differ in felids. A diet comprising lineolate but not arachidonate did not result in the presence of arachidonate in plasma lipids as it would in other mammals. This deficiency led to poor growth, skin lesions slow wound healing and poor reproductive performance amongst other things. (Rivers et al, 1975)
Vitamins and Minerals
Fat-soluble vitamin A is a dietary essential for all vertebrates and can exist preformed, as retinol and as a pro-vitamin, e.g. carotenoids. Felids are unable to convert carotenes to retinol. (Morris, 2001) Therefore they must consume vitamin A in its final form. Wild lions are provided with the required amount of retinal through the consumption of herbivore internal organs and muscle tissue. Retinol is fundamental for development, bone formation, gene expression and reproduction. (Gernshoff et al 1957)
Mineral requirements of felid species do not greatly exceed those of other mammals, and domestic cats have successfully developed and reproduced on a mineral mix similar to that of omnivores (rats and pigs)(MacDonald et al, 1983). Felids fed whole bodies of prey attain all essential minerals, however, when fed only soft tissues without the prey skeleton, a deficiency in calcium is acknowledged, leading to skeletal abnormalities and nutritional secondary hyperparathyroidism. (Fiennes & Graham-Jones, 1960)(Krook et al, 1963)
Water Requirements
Felids have evolved to obtain almost all their water requirements from the moisture content in their food. Clarke and Berry (1992) found that average water influx of wild lions was 49 ml/kg/day and suggested water from prey would constitute 60% and drinking 40% of this. Cats are able to concentrate their urine more than other dogs and humans (Chew, 1965) therefore are able to go long periods of time without drinking. This makes them susceptible to Feline Urological Syndrome (FUS) (Macdonald et al, 1984). A planned zoo diet must consider this and ensure lions are provided with enough water to drink or within food.
The table displays the nutritional requirements of carnivores on a dry matter basis (NRC, 2006)