Written by: Dr. Jacquie Jacob, University of Kentucky
Protease inhibitors are small protein molecules that have the ability to interfere with the action of the proteolytic enzymes involved in breaking down protein into amino acid components. The typical animal response to an intake of protease inhibitors is to increase enzyme secretions, which results in increased size of the pancreas (which secretes digestive enzymes into the duodenum).
Trypsin is an important enzyme in protein digestion in poultry diets. In poultry, trypsin inhibitors reduce the availability of amino acids. Trypsin inhibitors have been isolated from many legumes, including soybeans and field peas. Trypsin inhibitors can be destroyed by heat, which is why whole soybeans must be roasted before they can be included in poultry diets. Soybean meal, which is a by-product of soybean oil extraction, is a common ingredient in poultry diets.