# Standardized Amino Acid Digestibility Estimates of Individual Ingredients from Precision-Fed Cecectomized Roosters Are Additive

## TL;DR

This study shows that amino acid digestibility values from individual ingredients in pet food can be added together to predict digestibility in mixtures, using cecectomized roosters.

## Contribution

The study demonstrates that amino acid digestibility values from individual ingredients are additive and predictive in mixtures using a precision-fed cecectomized rooster model.

## Key findings

- All ingredients had standardized ileal indispensable amino acid digestibilities >85% except for lysine in corn-gluten meal.
- Amino acid digestibilities were highest for dehydrated egg and mixtures with higher egg inclusion.
- Measured and predicted amino acid digestibility values were similar for most mixtures, except for histidine and serine in one mixture.

## Abstract

Pet foods are typically not formulated based on indispensable amino acid (AA) digestibility values, but this strategy could be used to ensure nutritional adequacy while reducing the inclusion of protein-rich ingredients to improve sustainability. Cecectomized roosters are often used to determine the standardized ileal AA digestibilities of individual ingredients. It is also important to determine whether the digestibility values from individual ingredients are additive and predictive of AA digestibilities for ingredient mixtures. Our first objective was to measure the AA concentrations and digestibilities of dehydrated egg, pea protein, and corn-gluten meal (CGM) and their mixtures using the precision-fed cecectomized rooster assay. Our second objective was to determine whether the AA digestibilities of individual ingredients were additive for ingredient mixtures. All ingredients and mixtures had standardized ileal indispensable AA digestibilities >85% except for lysine in CGM. Standardized ileal AA digestibilities were typically higher for egg and mixtures with higher egg inclusion. There were no differences between measured and predicted AA digestibility values for all ingredient mixtures, except for histidine and serine in the 75% egg–25% CGM mixture. These data suggest that the standardized ileal AA digestibilities obtained from individual protein-based ingredients in precision-fed cecectomized roosters are additive and predictive of those in ingredient mixtures.

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.