Decreasing dietary crude protein in broiler chickens is a strategy known to have multiple benefits such as reducing N excretion, positively affecting intestinal health and reducing foot pad lesions. In addition, there is interest to increase the diversification of feed raw materials for broiler diets and to use more local alternative feed ingredients. This study evaluated the effect of full or partial replacement of SBM and crude protein (CP) reduction in the grower phase (14-36d of age) on the performance of broiler chickens. At 14 days of age, 324 Ross 308 male broilers were randomly allocated into 6 dietary treatments with 6 pens per treatment. Experimental diets were: A: control at 20.7% CP with 21%-SBM; B: 18.7% CP & 0%-SBM, C: 19.7% CP & 0%-SBM; D: 19.7% CP & 5%-SBM; E: 19.7% & 10%- SBM; F: 19.7% & 15%-SBM. All diets were isoenergetic and iso-digestible Lys and all the essential amino acids were at least at the level of the assumed requirement. In the low CP diets, inclusion of feed-grade L-Val, L-Arg & L-Ile was needed to balance the diets. In the zero or reduced SBM treatments, SBM was mostly replaced by sunflower (SFM), rapeseed (RSM) and some corn gluten (CGM) meal. Average daily feed intake (ADFI), average daily gain (ADG), feed conversion ratio (FCR) and final body weight (BWf) were evaluated and statistically analysed by 1-way ANOVA using BW at 14d and block as covariate. Birds were individually weighed at d36 and the coefficient of variation (CV) was calculated and statistically analysed. Between diets B, D, E and F, treatments only differed by SBM inclusion from 0 to 15% and therefore SBM inclusion effects were tested for linear and quadratic response.

From day 14 to 36, there was no significant (P>0.05) difference in ADFI (±149.3g/d), ADG (±105.8g/d), FCR (±1.41), BWf (±2803g) or CV (±8.1) across treatments. No significant (P>0.05) quadratic response was observed for any studied parameters. Reducing dietary SBM inclusion linearly (P<0.05) reduced ADFI and tended to reduce FCR (P=0.062).