Patterns and risk factors of pig transport mortality: implications for official controls in a high-throughput...

Transport to slaughterhouses is a critical phase in pig production, affecting welfare and economics. Mortality during transport, or dead-on-arrival (DOA), is a direct indicator of welfare compromise. This study evaluated the association between estimated transport distance, ambient temperature, and consignment size with mortality in commercial pig journeys lasting ≤ 8 h.

Data from 34,239 consignments from 434 farms transported to a high-throughput slaughterhouse were analyzed. Consignment size ranged from 5 to 164 pigs, estimated transport distances from 5 to 605 km, and ambient loading temperatures ranged from 0.9 °C to 31.2 °C. Overall average mortality rate was 0.062%, with 93.1% of consignments showing no DOA pigs. Seasonal patterns were pronounced, with summer exhibiting the highest mortality and winter/spring the lowest. Mixed-effects logistic regression showed that ambient temperature and estimated transport distance were positively associated with mortality (OR = 1.354 and 1.086, respectively), while larger consignments exhibited a negative association (OR = 0.910). Each 1 °C increase in temperature corresponded to a 3.86% rise in the odds of pigs being DOA. Random farm effects showed substantial between-farm variability. Average transport mortality per farm categorized 36.9% of farms as being at very low risk, 13.1% as low, 24.9% as medium, and 25.1% as high risk. Best Linear Unbiased Predictors (BLUP) estimates identified 38 farms with significantly higher-than-average mortality, while funnel plot analysis highlighted 26 outliers, providing complementary approaches to benchmark farm performance and prioritize high-risk holdings for welfare monitoring. Among 664 (1.95%) consignments inspected by official veterinarians, mortality was 0.036%, and inspections were evenly distributed across seasons, ambient temperatures, and consignment characteristics. Only 86 (12.95%) of inspections targeted the 26 high-risk farms identified by the funnel plot. These results suggest that inspection efforts were not preferentially directed toward farms with elevated predicted mortality.

Pig mortality during journeys lasting ≤ 8 h transports is mainly associated with ambient temperature and, to a lesser extent, estimated transport distance, with summer as a high-risk period. Larger consignments modestly reduce risk, and mortality per farm highlight the potential for targeted interventions. Current veterinary inspections are not systematically aligned with risk, suggesting scope to optimize monitoring and welfare outcomes.