It is important to determine whether amino acid (AA) digestibility values from individual ingredients are additive and predictive for mixed diets. This study had two objectives: (1) measure the AA concentrations and digestibilities of individual protein ingredients and their mixtures and (2) determine whether the AA digestibilities of the individual ingredients were additive in their mixtures. Forty-two cecectomized roosters were randomly allotted to one of seven ingredients: dehydrated egg (EGG); pea protein (PP); corn-gluten meal (CGM); a mixture of PP and EGG at a 25:75 ratio (PP25); a mixture of PP and EGG at a 75:25 ratio (PP75); a mixture of CGM and EGG at a 25:75 ratio (CGM25); and a mixture of CGM and EGG at a 75:25 ratio (CGM75). Endogenous loss corrections were made using five fasted additional cecectomized roosters. All ingredients had indispensable AA digestibilities >85% except histidine for CGM. Amino acid digestibilities were typically the highest for EGG, PP25, and CGM25. There were no differences between measured and predicted AA digestibility values, except for histidine and serine in CGM25 (p < 0.05). Our results suggest that all protein-based ingredients tested were highly digestible and that the AA digestibilities obtained from individual ingredients are additive in ingredient mixtures when using the precision-fed cecectomized rooster model.
Keywords: canine; digestibility; feline; protein additivity; protein ingredients; protein mixtures.