Managing Seasonal Infertility in Sows: Parity and Farm-Specific In-Barn Environmental Predictors of Reproductive Performance

Seasonal infertility remains a major challenge in pig production and is influenced by environmental conditions and sow parity. This study aimed to identify in-barn heat load (HL), light variability (LV), and parity as farm-specific predictors of farrowing success (FS) and litter size (LS) in purebred Large White sows raised under subtropical and tropical conditions in Brazil. Reproductive records from 2021 were obtained from two commercial farms, and in-barn temperature and illuminance were recorded using data loggers installed in gestation units. Services between March and August 2021 were analyzed using logistic regression for FS and linear regression for LS, resulting in 732 service records from Farm 1 and 233 from Farm 2. In the combined analysis, parity was associated with higher odds of FS (OR = 1.20; p = 0.003) and greater LS (β = 0.47; p < 0.001). HL was not associated with FS but showed a small positive association with LS (β = 0.28; p = 0.031). In Farm 2, LV was negatively associated with FS (OR = 0.72; p = 0.028) and LS (β = −0.59; p = 0.020). Overall, parity structure strongly shaped reproductive performance, and in-barn environmental effects were context-dependent.