Physiological stress and welfare of broiler chickens in transit: solutions not problems!

The rearing of large numbers of broiler chickens at geographically dispersed sites means that they have to be transported by road, over various distances, to centralized processing plants for slaughter. The birds may be exposed to a variety of stressors during transit, including the thermal demands of the transport microenvironment. The thermal environments experienced by broiler chickens during routine transport in the U.K. on a large number of commercial vehicles under a wide range of external climatic conditions have been characterized using three-dimensional thermal mapping (temperature and water vapor density). Inadequate ventilation results in heterogeneous distributions of temperature and humidity and, thus, thermal loads within the vehicle, and, therefore, the existence of a "thermal core" in which the risk of heat stress is increased. Relationships between specific physiological indices of stress and quantified thermal loads have been determined in accurate transport simulations in the laboratory. The findings have been employed to establish a predictive model of the induction of heat stress during commercial transportation, as well as to define the acceptable ranges and limits for temperature and humidity within the transport containers. These principles have been utilized in developing a monitoring system to warn of impending heat stress and in improving vehicle design to facilitate the prevention of heat stress during broiler transportation.