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

The influence of stocking density (16, 20 and 24 birds/m(2)) and zinc bacitracin (0 or 100 mg/kg) on the performance, carcass characteristics and some indirect welfare indicators of broilers were examined in a 35-day trial. The weight gain, feed intake, liveability and carcass characteristics of broilers grown at densities of 16, 20 and 24 birds per m(2) were similar (P > 0,05). Over the whole trial period, however, feed per gain of birds at the highest density (24 birds/m(2)) was higher (P < 0.05) than those at the other two densities. 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 weight gains and feed intake of broilers over the 35-day trial period at all three stocking densities tested, Zinc bacitracin supplementation had no influence on the feed per gain of birds reared at densities of 16 and 20 birds/m(2), but improvements were observed at a density of 24 birds/m(2). The relative weights of lymphoid organs (spleen and bursa) were lowered (P < 0.05) with increasing density, suggesting a greater degree of stress on the birds. Zinc bacitracin supplementation had no influence on bursa weights of birds reared at densities of 16 and 20 birds/m(2), but increased the bursa weights of birds reared at a density of 24 birds/m(2). Overall, these data indicate that, with the removal of in-feed antibiotics in the future, care should be taken when considering population densities of greater than 20 birds/m(2).