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

This study evaluated associations between thermal load and reproductive performance in commercial sow herds under contrasting housing systems in subtropical Taiwan.

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.

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).

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.