Evaluating the association between climatic factors and sheep condemnations in the United States using cluster analysis and spatio-temporal modeling

Sheep in the United States are primarily raised and fed on pasture, making them particularly susceptible to the impacts of climatic factors. This study sought to evaluate the association between climate and whole carcass condemnations in the U.S. as a proxy to evaluate overall sheep health across the U.S. USDA FSIS inspection data was evaluated for whole carcass sheep condemnations between 2005-2016. The analysis focused on condemnations attributed to caseous lymphadenitis, the most frequent cause of sheep condemnations during this period. Data was analyzed on the climate division scale - 344 subdivisions of the contiguous United States that divide states into nearly homogenous climatic regions. Using space-time cluster analysis for high rates of condemnations, ten clusters were identified ranging across the United States. All but one of these clusters was confined to single climate division, with lengths ranging from 1 to 72 months. A zero-inflated Poisson regression found significant associations between condemnation counts and precipitation, cooling degree days (an indicator of higher temperatures), year, and division of the United States. The model had a marginal R-squared of 0.54. This study has identified high risk clusters where higher than expected condemnations are concentrated. The confirmation of an association between climatic factors and condemnation numbers suggests that management practices targeted at protecting pasture-raised small ruminants from weather extremes would improve overall animal health and welfare. Mitigation strategies should be considered as we face increasing frequency of extreme weather events and other environmental fluctuations associated with climate change.