Chemical composition, true nutrient digestibility, and true metabolizable energy of novel pet food protein sources using the precision-fed cecectomized rooster assay

A wide variety of animal protein-based ingredients is commonly used in the pet food products. The raw ingredients and processing procedures used may greatly affect protein quality. Testing the quality of alternative protein sources is necessary and contributes to the sustainability of pet foods. The objective of this study was to test the chemical composition of 8 protein sources intended for use in dog and cat foods (calamari meal, pork peptone, alligator meal, lamb meal, venison meal, chicken meal, and 2 duck meals), and evaluate their true nutrient digestibility and nitrogen-corrected true ME (TMEn) using the precision-fed cecectomized rooster assay. Calamari meal and pork peptone had lower ash (4.4 and 3.6% of DM, respectively) but greater CP (88.1 and 80.5% of DM, respectively) and either greater or similar GE (5.6 and 5.3 kcal/g of DM, respectively) compared with alligator, lamb, venison, chicken, and duck meals (11.8 to 24.5% ash, 58.7 to 65.9% CP, and 4.6 to 5.3 kcal GE/g). Acid-hydrolyzed fat (AHF) was lower in calamari meal (8.7% of DM) compared with the other proteins tested (15.5-22.1% of DM). True nutrient digestibility was variable among the protein sources (52 to 79% of DM, 60 to 83% of OM, 78 to 92% of AHF, and 70 to 89% of GE) with pork peptone having the highest DM, AHF, and GE digestibility and calamari meal having the highest OM digestibility. True indispensable AA digestibility was highest for calamari meal, with all AA having a digestibility greater than 90%. Except for histidine, all indispensable AA had a digestibility over 85% for pork peptone. In contrast, true indispensable AA digestibility was lowest for lamb meal, with histidine having digestibility less than 70% and the other entire indispensable AA having digestibility between 72 and 88%. The TMEn of calamari meal (4.82 kcal/g DM and 86.9% of GE) was greater (P < 0.05) than the other protein sources. The lamb meal had the lowest TMEn value (3.12 kcal/g DM and 66.9% of GE), with others being intermediate (3.46-4.09 kcal/g DM and 71.2-77.9% of GE). This study demonstrates the considerable variability that exists not only in the chemical composition but also in the true nutrient digestibility among protein sources intended for use in dog and cat foods and justifies further in vivo testing of novel protein sources.