Multiple factors affect the risk of broiler injury and mortality during loading, transport, and lairage. These include the physical and pathophysiological condition of broilers before loading and the type of handling procedures used. The external environmental conditions have a major influence on the risk of mortality. Combinations of high stocking density, insufficient ventilation, and high temperature and humidity pose a risk of hyperthermia. Combinations of wet conditions, cold temperature, and air movement, increase the risk of hypothermia. However, protection from cold and wet conditions involves the use of side protection that restricts the trailer ventilation that can cause heat and moisture to build up in the load, increasing the risk of hyperthermia. Modular systems reduce the risk of injury and facilitate unloading into a lairage where temperature and ventilation can be controlled. The duration of loading, transport, and lairage increases the mortality risk. Deaths can occur during each stage and interactions between the duration of the preslaughter stages, the thermal environment, fasting, ill-health, and injury can reduce the physiological capacity of the birds to maintain homoeostasis resulting in exhaustion and death. Quality control and action on the identified risk factors should reduce injury and mortality during preslaughter handling and transport.

Some injuries to broilers occur during rearing, but most injuries occur during handling before slaughter. Records provided by a processing plant for loads transported over a 19-month period during 2009 and 2010 were examined. The median percentage of wing injuries per load was 5.7%; while injuries to the legs, breast or shoulders were all less than 1% per load. Risk factors for wing injuries were examined by considering the data from each load by handling event (i.e. loads originating from the same producer on the same date). A multilevel model with three levels: producer (n=86), handling event (n=1694) and load (n=4219) was fitted. The final model included: weight, sex, season, catching team, time of day at which loading began, speed of loading, and an interaction between speed of loading and time of day. Factors that reduced the risk of wing injuries were loading lighter birds, loads containing only cockerels and loading in the fall. The predicted percentage of wing injuries was relatively constant for slower loading speeds but was increased significantly when faster loading speeds were adopted during daytime (0700 to 1700 h). Identification of these risk factors can be used to adjust loading practices.

Multiple factors can affect the risk of bruising and mortality of broilers during loading, transport, and lairage. The risk factors affecting the percentages of broilers in each load that were “dead-on-arrival” (DOA) or bruised were studied from records provided by a processing plant, by undertaking direct observations during on-farm loading and then carrying out multivariable analyses. Selected loads between 2014 and 2015 from seven producers were included in the study. The median DOA per load was 0.13% (Q1 = 0.06, Q3 = 0.25, n = 212), the median total duration from loading to unloading was 8.6 h, and the external temperature ranged from −22 to 22 °C. Although it was not possible to adequately characterise thermal conditions within each load, the analysis indicated that the main risk factors for increased mortality were in spring and winter, an increased duration between loading and end of lairage, and a period of feed withdrawal before loading longer than 6 h. The risk of mortality increased with the weight of the birds and with an increase in rearing mortality. No relationships were found between the manner in which the broilers were handled and the percentages of DOAs or bruised birds.