Standardised ileal amino acid digestibility of grain legumes is comparable to soybean meal for broiler chickens

Abstract

The aim of the present study was to determine standardised ileal digestibility (SID) of nitrogen (N) and amino acids (AA) of faba bean, lupin, lentil, chickpea, field pea and soybean meal (SBM) for growing male broilers. Grain legumes were incorporated into experimental diets either raw or after being steam-conditioned at 80°C for 30 s. The assay diets were formulated to contain 150 g/kg crude protein with the test ingredient as the only source of protein. Meanwhile, basal endogenous AA loss was measured by using a N-free diet to estimate SID. From 21–24 days post-hatch, each diet was randomly allocated to four replicate cages (eight birds per cage) with a total of 384 Ross 308 male broiler chickens. On day 24, all birds were euthanised and ileal contents collected to determine SID. No effect (P>0.05) was observed for heat treatment on SID of AA for lentil, lupin and field pea, but variable effects were observed in chickpea and faba bean (P<0.05). The SID of N and all AA in SBM were not different (P>0.05) to that of raw lentil, but were greater (P<0.05) than that of raw field pea. No differences (P>0.05) were observed for SID of N and AA between raw lupin and SBM, apart from arginine, cysteine, glutamic acid and glycine which were greater (P<0.05) in lupin. In raw chickpea, only SID of isoleucine, leucine, methionine, alanine and tyrosine were lower (P<0.05) than that of SBM. This study suggested that the AA digestibility coefficients of raw lupin, lentil and chickpea were not different from SBM and may be used as a replacement. However, due to their lower AA content, an additional protein source or non-bound amino acids may be needed to form a balanced diet.