Performance and welfare of broilers as affected by stocking density and zinc bacitracin supplementation.

摘要

Effects of stocking density (16, 20 or 24 birds/m2) and zinc bacitracin (0 or 100 mg/kg) were investigated on the performance, carcass characteristics and some indirect welfare indicators of chickens in a 35 day trial. The wt. gain, feed intake, liveability and carcass characteristics of chickens grown at densities of 16, 20 and 24 birds per m2 were similar (P > 0.05). Over the whole trial period, however, feed per gain of chickens stocked at the highest density was higher than those at the other 2 densities (P < 0.05). Litter quality was poorer at high population densities, but there were no welfare implications as indicated by the lack of effect of density on gait scores and the incidence of hock and fat pad burns. Inclusion of zinc bacitracin improved wt. gains and feed intake of chickens during the 35 day trial at all 3 stocking densities. Zinc bacitracin supplementation had no influence on the feed per gain of chickens reared at densities of 16 and 20 birds/m2, but improvements were observed at a density of 24 birds/m2. The relative wt. of lymphoid organs (spleen and bursa) were reduced with increasing density (P < 0.05), suggesting a greater degree of stress on the chickens. Zinc bacitracin supplementation had no influence on bursa wt. of chickens reared at densities of 16 or 20 birds/m2, but increased the bursa wt. of chickens reared at a density of 24 birds/m2. Overall, data indicate that, with future removal of in-feed antibiotics, care should be taken when considering population densities of >20 birds/m2.