Effects of extrusion conditions on trypsin inhibitor activity of full fat soybeans and subsequent effects on their nutritional value for young broilers

1. Increasing proportions of soybeans in poultry diets have highlighted the importance of correct processing to inactivate the anti-nutritional factors present whilst maintaining protein quality. 2. Ground full fat soybeans (FFSB) were extruded using a Clextral laboratory model twin-screw extruder with 0·75 l/h of water and end barrel temperatures of 90, 110, 130 and 160°C resulting in trypsin inhibitor activities (TIA) of 14·8, 9·6, 4·5 and 1·9 mg/g sample. 3. The 4 extrudates were used at three different inclusion levels: 200, 400 and 600 g/kg semi-synthetic diet and fed to male Ross broiler chicks from d 19 to d 26. Digesta samples were taken for measurement of coefficient of ileal apparent amino acid digestibility (CIAD) and both pancreas and whole bird weights were measured. 4. Concentration of ileal apparent digestible lysine was increased from 10·53 to 17·63 g/kg FFSB by increasing extrusion temperature from 90 to 160°C. CIAD of lysine was also improved from 0·58 to 0·86. Other amino acids showed similar improvements in both their ileal apparent digestible concentration and CIAD. 5. Mean weight gain over 3 d increased linearly from 42 to 95 g per bird with increasing extrusion temperatures of FFSB. Pancreatic enlargement was evident after 6 d of feeding with FFSB processed at lower temperatures, even when the TIA level was at the recommended threshold of 4 mg/g. 6. The results emphasise the importance of controlled conditions during processing of FFSB for poultry diets and suggest that processing of FFSB in order to reduce TIA levels below 4 mg/g may provide significant benefits for broiler chicks.