Density allowances for broilers: where to set the limits?

Stocking density has critical implications for the broiler industry because higher returns can be obtained as the number of birds per unit space increases. Assigned densities have been primarily driven by cost-benefit analysis, but economic profit may come at the cost of reduced bird performance, health, and welfare if densities are excessive. These negative consequences are the primary reason for the increasing demands for guidelines that limit density allowances, even through legislation. Current recommended densities are rather variable, and therefore it is critical if guidelines are to be established that they be based on sound science. Published research consistently indicates that the health and welfare of broilers is compromised if space allowances drop below 0.0625 to 0.07 m2/bird (equivalent to about 34 to 38 kg/m2 depending on final BW). Negative consequences include reduced final BW, feed intake and food conversion, and greater incidence of foot-pad dermatitis, scratches, bruising, poorer feathering, and condemnations. A few studies have also found higher mortalities, tibial dischondroplasia, and some evidence of physiological stress. At the behavioral level, most studies indicate a reduction in space use and movement and higher frequencies of disturbances, which has been linked with a higher frequency of scratches and decline in carcass quality. Other main behavioral categories remain largely unchanged. However, results overwhelmingly suggest that while stocking density has major consequences for the health and welfare of broilers, the quality of the environment, which has been largely underestimated, is far more relevant. Advances in broiler welfare will be difficult to achieve unless some criteria for environmental quality are also established. The implications of this are that the welfare of broilers can be ensured at a range of (reasonable) densities, as long as the requirements for environmental quality are fulfilled. It is also essential for industry to realize that returns per unit of space in broiler production do tend to plateau if density is excessive, a result of the reduction in bird performance. In this paper I suggest a model that may be used to maximize productivity, health, and welfare.