The modified Atwater equation does not accurately predict diet ME value of premium food in adult cats

Abstract Text: The diet ME value of pet foods is commonly predicted using the Atwater equation, because routine ME measurements are not practical or not feasible ethically or financially. As such, AAFCO recommends the use of the modified Atwater equation [ME = 3.5×CP (%) + 3.5×N-free extract (NFE, %) + 8.5×crude fat (%)] to predict metabolizable energy (ME) of dog and cat foods, which is then used to calculate daily feeding allotment. Previously, the modified Atwater equation underestimated the measured ME value of dog diets; hence, we decided to study this equation in cats. Twelve domestic shorthair cats were used in a quadruple 3× 3 Latin square. Initial BW averaged 4.4 ± 0.8 kg and ranged from 3.0 to 5.7 kg. Three premium cat diets varying in predicted glycemic index (GI) based on ingredient composition and starch content (36.8, 30.7, and 23.6% for high, medium, and low GI, respectively) were fed for 10 d, with feces and urine collected quantitatively for the last 5 d. Diet, feces and urine were analyzed for GE to measure diet ME value. Predicted GI and ME value of the 3 diets were inversely related. The greater ME value of the low GI diet (P<0.001) was associated with its greater fat content (22.9,  22.2, and 15.7% ether extract for low, medium and high GI diet, respectively) and energy digestibility (95, 95.4, and 92.9% for low, medium and high GI, respectively). The modified Atwater equation underestimated measured diet ME values by 12% (11.9, 10.8, and 13.6% for high, medium, and low GI, respectively). The traditional Atwater equation [ME = 4×CP (%) + 4×N-free extract (NFE, %) + 9×crude fat (%)] did predict diet ME values accurately (underestimation of 2.0, 1.5, and 4.6% for high, medium, and low GI, respectively). In conclusion, the modified Atwater equation did not accurately predict diet ME value of diets fed to adult cats. The traditional Atwater equation should be used for premium cat diets.

Keywords: metabolizable energy, Atwater, cat