Abattoir surveillance of pneumonia and pleurisy in Western Australian sheep for 2016–2024

The ovine respiratory complex (ORC) is an important contributor to production losses and welfare concerns in sheep worldwide. This study examined trends in the detection of pneumonia and pleurisy in sheep from Western Australia, utilising abattoir surveillance data collected for the National Sheep Health Monitoring Project between 2016 and 2024. Trained meat inspectors inspected carcases and viscera from over 10 million sheep from 3989 farms and 4353 indirect consignments over the 9 years. Pneumonia was detected in 0.99 sheep per 1000 sheep inspected (95% confidence interval [CI] 0.96 to 1.01) and 41.0% of farms (95% CI 39.5 to 42.5). Pneumonia detection increased each year from 2021 (P < 0.05), with a 6.4‐fold increase in animal‐level detection and a 3.0‐fold increase in farm‐level pneumonia detection observed between 2021 and 2024 (P < 0.001). Pneumonia detection was higher during spring and summer and for sheep aged 2 years or older but did not differ between regions or consignment types. Pleurisy was detected in 12.4 cases per 1000 sheep (95% CI 12.3 to 12.5) and 87.3% of farms (95% CI 86.3 to 88.4). Pleurisy detection was 12.6‐fold higher at the animal level and 2.1‐fold higher at the farm level compared to pneumonia (P < 0.001). There was no increase in the detection of pleurisy between 2021 and 2024. Pleurisy detection was more common for sheep aged at least 2 years old and some regional differences were observed. This study demonstrates that ORC is widespread on Western Australian farms, underscoring the value of abattoir surveillance in identifying disease trends that can inform targeted interventions to improve sheep health, productivity and welfare.