Influence of the stocking density and rearing season on incidence of sudden death syndrome in broiler chickens.

Influences of the stocking density and rearing season on the incidence of sudden death syndrome (SDS) were investigated in commercial broiler chickens, which were reared until 63 d after birth. The SDS mortality and total mortality were measured at three different stocking densities of 12, 15, and 18 birds/m2 in rearing seasons of summer, autumn, and winter. At stocking densities of 15 and 12 birds/m2, neither SDS mortality nor total mortality was significantly different throughout the rearing season. However, at 18 birds/m2, SDS mortality significantly increased in summer and winter. The increased SDS mortality was accompanied by a significant increase in total mortality in summer but not in winter. Irrespective of the stocking density, body weight gain and feed intake were lower in summer with no significant change in feed efficiency. The data suggest that stocking density can act as a factor affecting the incidence of SDS in summer and winter, independent of feed efficiency.