Determining metabolizable energy content in commercial pet foods

This study was conducted to assess the suitability of several equations for the estimation of metabolizable energy (ME) of pet foods. Sixteen canned and 31 dry cat foods and 24 dry dog foods representing the range of energy densities found in commercial adult, growth or all life stage products were evaluated in four separate experiments. In vivo ME was compared with estimates of ME generated by several previously published equations. The results indicated that the equation recommended by Association of American Feed Control Officials provided reasonable estimates of in vivo ME for both canned cat foods and dry dog foods, but proved unsuitable for dry cat foods. Better estimates were generated in each case using other published equations. Of the equations tested, the most accurate equations for estimating ME (kJ/g) without feeding trials were: for canned cat foods: [(16.32 x protein) + (32.22 x fat) + (12.55 x NFE)]; for dry cat foods: [((GE x 1.209) - 1.911) x 4.184] or [((0.075 x g fat) + 2.766) x 4.184] for dry dog foods: [GE=(24 x g protein) + (38 x g fat) + (17 x g NFE), then percentage energy digestibility=91.2 - (1.43 x percentage crude fibre in dry matter), then ME=(GE x percentage energy digestibility) - (4.34 x g protein)]. With the exception of high-fibre weight-management diets, the simple equation [((GE x 1.209)-1.911) x 4.184] also reliably predicted ME in dry dog foods.