The potential for the improvement of the nutritive value of soya-bean meal by different proteases in broiler chicks and broiler cockerels

1. The potential for improving the nutritive value of commercial solvent-extracted, heat-treated soya-bean meal (SBM) by protease treatment was measured using growing broiler chicks and tube-fed broiler cockerels. 2. SBM was pre-treated (50 degrees C for 2 h) with water alone; at alkaline pH (initial pH 8.25) with and without protease P1 (isolated from a Bacillus species) or at acid pH (initial pH 4.5) with and without protease P2 (isolated from an Aspergillus species) and incorporated into diets (290 g SBM/kg diet) for broiler chicks (20 chicks/treatment). Only protease P2 treatment improved chick performance; from 7 to 28 d of age, chicks fed on treated SBM had greater feed intakes and gained more weight than chicks fed on untreated SBM. Both proteases P1 and P2 significantly reduced chick serum anti-soya antibodies while protease P2 treatment increased apparent ileal nitrogen (N) digestibility and apparent N retention across the whole digestive tract. 3. Two tube-feeding experiments established that, of the treated SBMs used in experiment 1, only protease P2 treatment improved apparent N digestibility and true metabolisable energy. Also it was shown that increasing the temperature at which treated SBM was dried to 60 degrees C, compared with freeze-drying or drying at 50 degrees C reduced apparent N digestibility and true metabolisable energy of SBM with no significant interactions between enzyme treatment and drying temperature for both apparent N digestibility and TME. 4. It is concluded that, overall, the nutritional value of SBM assayed in a growth trial and by tube feeding was improved by treatment with protease P2 and not by treatment with protease P1.