Modelling broiler chicken health and welfare in a changing climate
Agriculture is particularly exposed to climate change, which threatens global food security. To date, climate change impact assessments on future food availability have focussed primarily on crop production. Projections of climate change impacts on livestock are relatively rare, with productivity gains and losses yet to be fully quantified. This thesis aimed to quantify and project the impacts of climate change on loss of market weight broiler (meat) chickens due to poor health and welfare at slaughter. Focussing on the mild temperate climate of Great Britain (GB), this thesis considered how weather has impacted on the health and welfare of commercial broiler chickens in the past, and how changing weather patterns in GB might impact on broiler health and welfare in the future. An environmental epidemiological approach and methodology was applied to an extensive slaughterhouse dataset shared by the Food Standards Agency, UK, and to historical weather and climate projection data obtained via the Met Office and Centre for Environmental Data Analysis. A descriptive epidemiological analysis of 16 health and welfare conditions, recorded during routine ante- and post-mortem inspections in slaughterhouses across GB, was used to identify those conditions most likely to be affected by weather. Daily counts of ascites (a common metabolic disorder) and abnormal colour/fever (septicaemia/toxaemia: a systemic bacterial infection) were examined in relation to outdoor temperature throughout broilers’ lifespan by means of time-series regression; a statistical approach rarely utilised in animal welfare science. A distributed lag non-linear model defined the U-shaped relationship between daily mean temperature and day-to-day changes in the number of broilers found dead on arrival or dead in the lairage (DOA) at slaughter. This information was applied to UK climate projections (UKCP18) to estimate temperature-related death losses of market weight broilers in Central England during 2040s (compared to 2010s) under two alternative climate change scenarios (RCP2.6 and RCP8.5). Risk of abnormal colour/fever was found to increase as mean temperature dropped below 0℃ on the day of slaughter. Risk of ascites increased as mean temperature rose above 15℃, on the day of slaughter and day 9 before slaughter. Hot (≥16℃) and cold (≤ 2℃) temperature extremes on the day of transport to slaughter were associated with an increased risk of DOA, while hot temperature 2 days before transport appeared to protect against DOA. Temperature-attributable DOAs were projected to increase by mid-century, with 4.5 times greater losses projected under a strict global strategy to mitigate greenhouse gas (GHG) emissions (RCP2.6) than with minimal effort to reduce emissions (RCP8.5). Findings suggest that commercial broiler chickens in GB are not afforded sufficient protection from environmental exposures during the transport process to slaughter, with implications for animal welfare, farmer profit, and food security. As our climate continues to change, improvements to transport management and/or facilities are likely to become increasingly necessary to improve the welfare and survivability of broiler chickens at the final stage of production. This thesis concludes with recommendations for industry, policy, and follow-on research, and highlights the great potential for advancements in modelling within animal welfare science.
Animal welfare, broiler chicken, livestock production, weather, outdoor temperature, climate change, food security, statistical modelling, environmental epidemiology, ascites, dead on arrival, septicaemia
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