Effects of single and twin thermal screw extrusion on protein quality of grain-free pet foods formulated with predominantly animal- or plant-based protein ingredients

With the diversification of the pet food industry and increasing market demand, the inclusion of plant protein in companion animal diets has become of interest. Pulses, commonly seen in grain-free diets, are high in protein and could serve as an alternative source of animal-based protein. There has been research on the ingredient about nutrient profiles and effects on canine health. However, little is known about the amino acid availability when pulses are incorporated into diets. In addition, there is lacking in knowledge about the effect of extrusion processing on protein quality and the possible interaction between processing and ingredients. Therefore, the study was conducted to determine the effect of extrusion and pulses on amino acid digestibility and protein quality. Eight grain-free diet formulations were designed: chicken byproduct meal diet (CON), chicken slurry diet (SLR), chicken slurry + yellow pea diet (SLR+YP), yellow pea diet (YP), green lentil diet (GL), garbanzo bean diet (GB), chicken slurry + taurine diet (SLR+TAU), and chicken slurry + yellow pea + taurine diet (SLR+YP+TAU). Two types of extruders were used: single screw and twin screw extruder. Diet samples were taken at 3 processing time points: raw ingredients, at the end of the preconditioner, and at the end of the extruder. The resulting 48 diet samples were analyzed for chemical composition and fed to cecectomized roosters (n=4/treatment) to determine standardized ileal amino acid digestibility and Digestible Indispensable Amino Acid Score (DIAAS)-like values. Even though the diets were mostly similar in chemical composition, methionine content was lower in diets containing yellow pea and green lentil. Extrusion processing did not have negative effect on natural or synthetic taurine in the diets. Preconditioning and extrusion also increased amino acid digestibility and DIAAS-like values in most diets, as processed diets could be considered well-digested and of good protein quality. According to reference protein sources, tryptophan and methionine were the most limiting amino acids in all treatment diet samples. In conclusion, grain-free diet formulation could result in good protein quality in canine diets and extrusion processing increased amino acid digestibility and protein quality.