URBANA, ILL. — With increased interest in the inclusion of plant-based ingredients, namely pulses, in pet food formulas, a new study has examined the effects of extrusion on such ingredients. 

The study, entitled “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,” was conducted by Clare Hsu, Pamela L. Utterback, Carl M. Parsons and Maria R.C. de Godoy all of the Department of Animal Sciences at the University of Illinois at Urbana-Champaign, as well as Gary M. Davenport of ADM, and Galen Rokey of Wenger Manufacturing. 

Plant-based ingredients have gained popularity throughout the industry as processors look to provide more sustainable options. Pulses have largely been used for their high protein and environmental benefits, however, according to the researchers, little is known about the amino acid availability and digestibility of pulses, and the impacts of extrusion on protein quality. 

The study consisted of creating eight grain-free formulas for dogs using various levels of animal- and plant-based proteins. Each diet was made as complete-and-balanced in accordance with the Association of American Feed Control Officials (AAFCO) recommendations. Ingredients for the diets were sourced and mixed at ADM Nutrition Center in Effingham, Ill. Each formula was made using a single screw and a twin screw extruder at Wenger’s Pilot Plant in Sabetha, Kan.  

The formulas included: 

  • chicken byproduct meal diet
  • chicken slurry diet
  • chicken slurry and yellow pea diet
  • yellow pea diet
  • green lentil diet
  • garbanzo bean diet
  • chicken slurry and taurine diet
  • chicken slurry, yellow pea and taurine diet

The foods that contained pulses had pulse inclusion rates of 400 g per kgs. 

Researchers collected samples from each formula at three points of processing: raw ingredient, at the end of the preconditioner, and at the end of the extruder. Samples were then analyzed for their chemical composition and fed to cecectomized roosters to determine amino acid digestibility. 

The researchers noted that preconditioning and extrusion increased the amino acid digestibility of most of the diets. Additionally, extrusion did not have a negative impact on natural or synthetic taurine. Though all the diets were similar in chemical composition, the researchers highlighted that methionine content was lower in the diets containing yellow pea and green lentil. 

“According to reference protein sources, tryptophan and methionine were the most limiting amino acids in all treatment diet samples,” the researchers wrote. “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.”

Read the full study here.  

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