186 Amino Acid Digestibility of Various Protein-Based Ingredients Using the Precision-Fed Cecectomized Rooster Assay
Authors: Oba Patricia Massae , Utterback Pamela L , Parsons Carl M , Swanson Kelly S 
Published: November 2023

Given their high protein quality and sustainable production practices, there is growing interest in using single cell-based proteins in pet foods. Because there has been a lack of testing on these proteins, the objective of this experiment was to determine the amino acid (AA) digestibilities of a single cell protein and other protein-based ingredients using the precision-fed cecectomized rooster assay. Test ingredients included: Calysta microbial protein (MP), chicken meal (CM), corn gluten meal (CGM), pea protein (PP), and black soldier fly larvae (BSFL). All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee prior to experimentation. Thirty cecectomized roosters (n = 6/ingredient) were randomly assigned to test ingredients. After 24 h of feed withdrawal, roosters were tube-fed 15 g of test ingredient and 15 g of corn. Following crop intubation, excreta were collected for 48 h. Endogenous corrections for AA were made using 5 additional cecectomized roosters. Digestible indispensable AA score (DIAAS)-like values were calculated to determine protein quality according to AAFCO nutrient profiles, FEDIAF nutritional guidelines, and NRC recommended allowances for adult dogs, adult cats, growing puppies, and growing kittens. Data were analyzed using the Mixed Models procedure of SAS 9.4, with P &lt; 0.05 being significant. All of the reactive lysine:total lysine ratios, an indicator of heat damage, were greater than 0.9 except for CM (0.86). All indispensable AA had digestibilities &gt;85% for MP, with indispensable AA digestibilities being &gt;80% for all ingredients. In general, CGM had the greatest AA digestibilities, while CM had the least AA digestibilities. Two exceptions were the digestibilities of lysine and tryptophan, which were greatest in MP. Lysine digestibility for MP (92.3%) was greater (P &lt; 0.01) than that of all other ingredients. Tryptophan digestibility for MP (97.2%) was greater (P &lt; 0.0001) than that of CM, CGM, and PP. Threonine and valine digestibilities were also greater for MP. Threonine digestibility was greatest for CGM (91.0%) and MP (88.6%), being greater (P &lt; 0.0001) than that of the other ingredients. Valine digestibility was greatest for CGM (93.3%), PP (89.3%), and MP (89.3%), being greater (P &lt; 0.001) than that of CM. DIAAS-like calculations estimated the protein quality of each ingredient, with the limiting AA of each depending on the reference used (NRC; AAFCO; FEDIAF) and life stage (growing; adult) and species (dog; cat) of animal in question. For dogs, limiting AA were most commonly methionine, threonine, and tryptophan. For cats, limiting AA were most commonly lysine and methionine. Further research in dogs and cats is necessary to confirm sufficient palatability and digestibility. However, our data suggest that the MP tested is a high-quality protein source with high AA digestibilities, and may serve as a valuable protein alternative for pet foods.