ABSTRACT
As indicated in the introduction, a second major topic regarding broiler welfare is the stocking density at which the birds are kept, usually expressed in kilograms of live weight per metre squared. Broilers are kept at relatively high stocking densities of over 15 birds/m2 or 30 kg/m2. Towards the end of the growing period, when birds approach slaughter weight and activity levels are low, these high stocking densities can lead to welfare problems. Especially in systems with poor management or housing conditions, high stocking densities can lead to poor litter quality and welfare problems, such as poor leg health and increased mortality rates. However, an influential study by Dawkins et al. (2004) showed that broiler welfare is in fact influenced more by housing conditions and farm management than by stocking density per se. They studied broiler welfare at ten major broiler-producing companies in the United Kingdom. For the study, each producer managed flocks at five different stocking densities, ranging from 30 to 46 kg/m2. Although there were clear differences in welfare indicators across flocks and producers, these could not be linked to stocking density. Factors such as litter moisture and air ammonia had strong effects on the welfare indicators measured, but some producers also managed to maintain a good litter quality and broiler welfare at the higher stocking densities. A critique on the study by Dawkins et al. (2004) has been that the low stocking density of 30 kg/m2 was still too high to see any major effects, as earlier studies including stocking densities lower than 30 kg/m2 did find clear effects on behaviour and welfare (Bessei, 2006). Having said that, the study by Dawkins et al. (2004) does underline the importance of good management: in a modern, well-ventilated and well-heated house with good management it is possible to keep broilers at a higher stocking density than in more basic housing systems. In the European Union, this has led to a rather unique Council Directive (2007/43/EC), where for the first time in history animal-based welfare measurements are included in the legislation. In that Directive, stocking density in broilers is limited to 33 kg/m2. Only if the producer can show that the company can manage broilers at a higher stocking density without high mortality for seven subsequent flocks (mortality below 3.5% for a slaughter age of 42 days), the producer can be allowed to keep broilers at a higher stocking density of maximum 39 kg/m2. The legislation also includes specifications about temperature, ammonia and humidity levels inside the house and includes a welfare inspection at slaughter, focusing on signs of footpad dermatitis, parasitism and systemic illness at the farm of origin. This seems a promising direction for legislation on animal welfare: by focusing on animal-based parameters at the farm or at slaughter, more precise information regarding the actual welfare status of the animals can be obtained, compared with just focusing on stocking density or other more descriptive parameters.
