Amino acid digestibility and protein quality of fermented soybean-based ingredients using the precision-fed cecectomized rooster assay

Soybean meals, soy protein isolates, and other forms of soy have served as protein sources in pet foods for many years. The amino acid (AA) content and protein quality of soybean-based ingredients vary depending on their composition and processing, however, so the testing of new ingredients is required. Our objective was to measure the AA composition, AA digestibility, and protein quality of fermented soybean-based ingredients using the precision-fed cecectomized rooster assay. Cecectomized roosters were randomly allotted to one of five test ingredients (n = 6/ingredient): 1) autoclaved soybeans (ASB); 2) fermented soybeans (FSB); 3) fermented soybeans + Lactococcus lactis subsp. lactis ATCC 11454 (FSBP); 4) fermented soybean meal (FSBM); and 5) fermented soybean meal + L. lactis (FSBMP). After 26 h of feed withdrawal, roosters were tube-fed test ingredients. Following crop intubation, excreta samples were collected for 48 h. Endogenous losses were accounted for by using 5 additional fasted cecectomized roosters. In addition to calculating AA digestibility, digestible indispensable AA score (DIAAS)-like values were determined and first limiting AA were identified based on dog and cat nutrient requirements or recommendations from the National Research Council (NRC). All data were analyzed by the Mixed Models procedure in SAS version 9.4. All ingredients had acceptable AA digestibilities, with all indispensable AA digestibilities being >80%, with the exception of histidine (79.3%), lysine (73.5%), and valine (79.0%) for ASB. All AA digestibility values were different (P < 0.05) among ingredients, with FSBP usually being the most digestible and ASB usually being the least digestible. The DIAAS-like values were highest for FSBP. The criteria for a high-quality protein source for adult cats was met by FSB, FSBP, FSBM, and FSBMP, with ASB meeting the criteria for a good-quality protein. The DIAAS-like values based on NRC recommendations for adult dogs, growing puppies, and growing kittens were lower. For adult dogs, growing dogs, and growing kittens, methionine + cystine was the first limiting AA. For adult cats, phenylalanine + tyrosine was first limiting. Differences existed, but our results show that fermented soybean-based ingredients have moderately high AA digestibilities and may serve as adequate proteins in pet foods.