Effects of variability in trypsin inhibitor content of soya bean meals on true and apparent ileal digestibility of amino acids and pancreas size in broiler chicks

Variability in the nutritional value of processed soya bean meal (SBM) and full fat soya bean (FFSB) currently restrict its use in diets for non-ruminant livestock. Two metabolism trials determined the amino acid digestibility and effect on pancreas size in young broilers of eight commercially obtained products. Trypsin inhibitor (TI) values varied from 1.1 to 3.6 mg/g but were all within the tolerated range of trypsin inhibitor activity (TIA). The results of the trials reported demonstrated that the coefficients of digestibility for individual amino acids varied widely between samples (e.g. coefficient of ileal apparent digestibility (CIAD), for lysine was from 0.755 to 0.884 for SBM and 0.778 to 0.848 for FFSB) but did not correlate with TIA levels, indicating other factors also affect amino acid digestibility of FFSB and SBM. Pancreas to body weight ratio (PBWR) increased with rate of soya inclusion in both the SBM (from 2.25 to 2.44 g pancreas/kg body weight) and the FFSB (from 2.19 to 2.40 g pancreas/kg body weight). The linear increase in pancreas size with increasing TIA intake suggested a dose dependent response that should be considered in feed formulation.