Amino acid digestibility of yellow mealworm-based ingredients using the precision-fed cecectomized rooster assay

Yellow mealworms (Tenebrio molitor) serve as an alternative for traditional protein sources (e.g., chicken, beef, pork). Because the amino acid (AA) concentrations, AA digestibility, and protein quality of ingredients vary depending on husbandry, harvest and processing procedures, and other factors, each should be evaluated separately. The objective of this study was to measure the AA composition, AA digestibility, and protein quality of yellow mealworm-based ingredients using the precision-fed cecectomized rooster assay. Eighteen cecectomized roosters were randomly allotted to one of three test ingredients (n = 6/group): 1) defatted yellow mealworm flour without cuticles (TM); 2) defatted yellow mealworm flour with cuticles (TMc); and 3) whole yellow mealworm pulp (TMp). After 26 h of feed withdrawal, roosters were tube-fed test ingredients (15 g ingredient + 15 g corn). Following crop intubation, excreta was collected for 48 h. Endogenous loss corrections for AA were made using five additional cecectomized roosters. In addition to calculating AA digestibility, digestible indispensable AA score (DIAAS)-like values were determined and limiting AA were identified based on dog and cat nutrient requirements or recommendations from the Association of American Feed Control Officials (AAFCO), European Pet Food Industry Federation (FEDIAF), and National Research Council (NRC). All data were analyzed by the Mixed Models procedure in SAS version 9.4. All ingredients were highly digestible, with all indispensable AA digestibilities being > 90%, with the exception of histidine (89.55%) and valine (89.36%) for TMc. Histidine digestibility was higher (P < 0.05) for TM and TMp than for TMc. Isoleucine, leucine, lysine, and valine digestibilities were higher (P < 0.05) for TMp than TMc. The DIAAS-like values were highest for TM, which scored high enough to be considered a high-quality protein source for most guidelines and life stages, with DIAAS-like values for TMc and TMp being slightly lower. For dogs and growing puppies, methionine or threonine were the limiting AA depending on reference guideline and life stage. For cats and growing kittens, arginine or methionine were the limiting AA. Even though there were slight differences among ingredients differing in composition (with or without cuticles; whole or defatted), our results demonstrate that yellow mealworm-based proteins have high AA digestibilities and protein quality, making them suitable proteins for pet foods.