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114 Evaluation of Extrusion Processing Method and Protein Source on Standardized Amino Acid Digestibility


 While the majority of dry complete and balanced foods for pet animals are extruded, the interaction between ingredient matrix and processing methods and stages are poorly understood. Thus, the objective of this study was to determine how the use of plant-based and poultry-based proteins processed under different extrusion condition may affect amino acid digestibility in extruded canine diets using a rooster model. Eight diet formulas were made using chicken (CK), chicken byproduct meal (CM), yellow pea (YP), green lentil (GL), and garbanzo bean (GB) as the primary protein sources. These diets were extruded through a single-screw and a twin-screw extruder. Food samples were collected at various stages of processing (i.e., raw, and after preconditioner, extruder, drier, and coating). Four cecectomized single-comb White Leghorn roosters were used for each diet sample. The roosters were fasted for 26 h and then fed with the treatment diets. The excreta were collected 48 h after feeding. Freeze dried excreta were used to calculate standardized amino acid digestibility (SAAD). For all essential amino acids, a significant interaction (P < 0.05) between diet and processing method was observed. The SAAD of arginine, tryptophan, and methionine were greater than 80% for all diets collected at the end of the extruder. The CK diet supplemented with synthetic taurine and processed through twin-extrusion had 70% to 80% SAAD of histidine, isoleucine, leucine, lysine, phenylalanine, threonine, and valine. Overall, twin-screw extrusion resulted in lower SAAD for all essential amino acids (P < 0.05), except for isoleucine and valine. However, the differences were smaller than 2.5%, and therefore may not negatively impact diet formulation and final product nutrient composition or guaranteed analysis. In addition, the extruded canine diets made with plant-based protein did not have lower amino acid digestibility than those made with animal-based protein.