Published in Animal Feed Science and Technology, the study also showed that extrusion did not compromise natural or synthetic taurine content in canine diets and that overall protein quality in pet food improves post-extrusion compared to raw ingredients.
Traditionally, animal protein has been the primary protein source in the pet food industry. However, with the diversification of market needs, alternative protein sources have been incorporated into pet diets. Plant proteins have gained appeal, and research has shown they provide sufficient quality to meet animals' nutritional needs, as demonstrated by in vivo digestibility studies in pets, outlined the researchers, based at the Department of Animal Sciences, University of Illinois at Urbana-Champaign, ADM, and Wenger Manufacturing Inc.
On the pulse
Pulses have become a focus of recent studies, especially after the US Food and Drug Administration (FDA) report on dilated cardiomyopathy in 2018. Although no concrete correlation has been established between grain-free diets and dilated cardiomyopathy, research has offered more insights into the nutrient profiles and availability of these alternative protein ingredients, claim the authors.
Pulses typically contain 200–280 g/kg (dry matter basis [DMB]) of crude protein, 290–350 g/kg (DMB) of dietary fiber, and 20–60 g/kg (DMB) of fat content. They are also economically accessible ingredients (FAO, 2016), commonly used as carbohydrate and/or protein sources in pet foods. However, the researchers maintain that little is known about the amino acid availability when pulses are included in diets.
Extrusion is the most widely used method of manufacturing pet food, with dry canine diets accounting for 57% of market sales in pet foods in the US. Despite this, the industry lacks comprehensive knowledge about the effect of extrusion processing on protein quality and the possible interactions between processing and ingredients, noted the authors.
So the team set about determining the effect of extrusion and pulses on amino acid digestibility and protein quality and assessing the effect of extrusion on taurine concentration in diets.
Study design
The researchers designed eight grain-free diet formulations: 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 in the study: single-screw and twin-screw extruders.
Diet samples were taken at three processing stages: 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 precision-fed rooster assay was used to assess standardized ileal amino acid digestibility and Digestible Indispensable Amino Acid Score (DIAAS)-like values.
Findings
Despite the diets being mostly similar in chemical composition, methionine content was lower in diets containing yellow pea and green lentil. Extrusion processing did not negatively affect natural or synthetic taurine levels in the diets. Preconditioning and extrusion significantly increased amino acid digestibility and DIAAS-like values in most diets, found the researchers.
"The amino acid profiles, including taurine concentration, within the same formula remained constant throughout the processing procedures. This could be an indicator that the heat and mechanical shear from extrusion did not degrade the amino acids, including taurine which has been associated to dilated cardiomyopathy, in the grain-free diets."
The first and second limiting amino acids for all diets were tryptophan and methionine, regardless of formulation, extruder type, or processing point.
“Even though the amino acid profiles of all the test diets met AAFCO guideline, additional tryptophan and methionine could be added to the formulas to increase the protein quality of the diets,” cautioned the team.
The researchers concluded that grain-free diet formulations can result in good protein quality in canine diets, and extrusion processing enhances amino acid digestibility and protein quality.
Source: Animal Feed Science and Technology
Title: 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
Authors: C Hsu, PL Utterback, CM Parsons, GM Davenport, G Rokey, M RC de Godo
