Thermal stress responses and reproductive stability in commercial sow herds under open-side and evaporative cooling systems in subtropical Taiwan.

OBJECTIVE: This study evaluated associations between thermal load and reproductive performance in commercial sow herds under contrasting housing systems in subtropical Taiwan. METHODS: Reproductive records from seven commercial pig farms (three open-side and four evaporative-cooling) were analyzed from January to August 2023. Temperature and relative humidity were continuously monitored to calculate the temperature-humidity index (THI). Linear mixed-effects models with farm as a random intercept were complemented by housing-stratified, segmented, generalized additive, lag-specific, variability, and multivariate analyses. RESULTS: Increasing THI was associated with lower farrowing and pregnancy rates and a higher stillbirth rate (p<0.001). Per unit increase in THI, farrowing and pregnancy rates decreased by 0.511 and 0.390 percentage points, respectively, whereas stillbirth rate increased by 0.241 percentage points. Open-side housing was associated with a 2.606-percentage-point lower farrowing rate than evaporative cooling (p=0.042), whereas the THI×housing interaction tests provided little evidence of differential linear THI associations between housing systems. Open-side barns also exhibited greater temporal variability in reproductive traits (p≤0.002) and greater multivariate dispersion (PERMDISP, p<0.001). CONCLUSION: Higher THI was associated with poorer reproductive performance. Reproductive performance was comparatively more stable in evaporative-cooling barns; however, housing-related differences should be interpreted cautiously because housing type was confounded with farm.