Factors affecting digestibility and in-vivo energy content of cat foods

Apparent digestibility and digestible energy (DE) content of 43 canned and 28 packeted samples of commercial cat foods were determined using panels of six adult domestic cats. Metabolizable energy (ME) content was also measured with 22 of the canned and 14 of the packeted foods. Mean apparent crude protein (CP), acid ether extract (AEE) and nitrogen-free extract (NFE) digestibility percentages of all foods (N = 71) were 78, 77 and 69. Apparent AEE and CP digestibility percentages increased in a curvilinear manner with intake; logarithmic regression curves explained 50 and 24 per cent of the variation in AEE and CP digestibility by intake. The use of modified Atwater factors over-estimated ME content of canned and packeted foods by 21 and 27 per cent respectively, compared with in vitro values. Twenty-one single or mulitple regression equations were generated predicting in-vivo DE or ME content of foods from laboratory analyses. The use of such equations in the practical definition of energy content of cat foods is discussed.