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The occurrence of bushfires (wildfires) is increasing with climate change in many areas of the world. In Australia, the 2019/20 bushfire season involved a particularly severe and widespread fire emergency (the 'Black Summer' bushfires). Understanding of how exposure to bushfires affects specific disease processes in livestock is limited. This research investigated spatiotemporal relationships between exposure to bushfires and observations of pneumonia and pleurisy in slaughtered sheep, and meat quality in slaughtered cattle. Two related cross-sectional studies were undertaken using historical abattoir monitoring data from the National Sheep Health Monitoring Project and the Meat Standards Australia Program. The study area involved the Australian states of New South Wales and Victoria, and the Australian Capital Territory, which were heavily affected by the 'Black Summer' bushfires. Carcase data were matched to fire occurrence data and to potential confounders including rainfall, pasture growth and pasture biomass indices for the farm of origin. The predictive approach to modelling included generalised additive mixed effects models and a generalised linear mixed model. Consistent though imprecise trends in pneumonia occurrence in sheep carcases were observed across time and distance since exposure to fire, with sheep slaughtered in the immediate aftermath of exposure to high intensity fires at a close distance having the highest occurrence (3.78 cases per 1000 sheep slaughtered 5 days after exposure to medium-to-high intensity fire at 0.5 km distance (95% CI 0.48, 30.02), compared to 0.387 cases per 1000 slaughtered sheep (95% CI 0.147, 1.02) across the study population). However, the economic implications of this for producers and processors are considered to be very limited. No such trends were observed in regards to pleurisy occurrence in sheep. Consistent trends were observed in meat quality in cattle carcases, with lower meat quality scores observed in cattle slaughtered after close proximity to fire (mean MSA index of 57.12 for cattle slaughtered 5 days after exposure to medium-to-high intensity fire at 0.5 km distance (95% CI 56.91, 57.34), compared to a mean of 57.65 (95% CI 57.60, 57.71) across the study population). In the aftermath of exposure to mid-to-high intensity fires, this may warrant consideration in withholding cattle from slaughter from an economic perspective, after decisions based on welfare grounds have been made. These observations will inform practical recommendations to improve health and productivity outcomes in management of bushfire-affected livestock. The observed trends may reflect causal relationships, but this requires further investigation with specific explanatory modelling studies. |
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