The value of a retrospective analysis of slaughter records for the welfare of broiler chickens

The effects of transport risk factors on deaths on arrival (DOAs; %) and carcass rejections (%) on broiler chickens transported to a slaughterhouse in Southern Spain were assessed using information routinely collected at the slaughterhouse. A total of 2,284 flocks and 10,198,663 broiler chickens, transported in 2,103 commercial transports from 217 different farms to a single slaughterhouse, were studied using the information of veterinary service and slaughter records. Studied risk factors were transport condition at arrival score (good/bad) and plumage condition score (good/bad) at arrival at the slaughterhouse, mixing loads (yes/no), transport duration (min), and season of the year (spring/summer/autumn/winter). Generalized linear mixed models were used to determine the effects of risk factors and their interactions on DOA and carcass rejections. The interactive nature of risk factors affecting both variables was revealed. Mixing loads interacted with transport duration (P < 0.0001), amplifying the negative consequences of long transports on DOA. Mixing loads also interacted with transport conditions at arrival (P = 0.0005), with the impact of bad transport conditions at arrival being particularly negative in the case of mixed loads. These facts raise questions about the suitability of mixing loads both from the animal welfare and economic standpoints. Transport duration interacted with season (P = 0.0003), with the detrimental effect of long distances on DOA being particularly evident during summer and winter, which highlights the need for alternative management measures when hot or cold temperatures are foreseen during transport. Long transports also increased carcass rejections (P < 0.0001). Mixing loads and bad plumage condition exacerbated the overall, detrimental effect of autumn transports on DOA (P = 0.0084 and P = 0.0009, respectively) with respect to summer transports. Similar results were obtained for the interactions between mixing loads and transport season (P = 0.0043) and transport conditions at arrival and transport season (P = 0.0014) on carcass rejections. Overall, results highlight the value of slaughter records to produce information useful to reduce the impact of transport risk factors, improve broiler chicken welfare, and improve slaughterhouse economic results.