Effect of temperature and humidity on sperm production in Duroc boars under different housing systems in Thailand

The aim of this study was to investigate the variation in temperature and humidity during a 12-month period in boar stables in Thailand with either conventional open air system (CONV) or evaporative cooling system (EVAP), as well as the effect of season, temperature, humidity, age of the boar, and semen collection interval on sperm production in Duroc boars kept in these stables. Ejaculates were collected from sexually mature Duroc boars in six CONV herds and five EVAP herds during a 1-year period. A total of 15,630 semen records were included in the statistical analyses. Temperature was higher and humidity was lower in the CONV system compared to the EVAP system. Twenty-one days moving-average of daily maximum temperature and minimum humidity with 7 and 14 days lag time was calculated and merged with each semen record. Besides the fixed effects included in the statistical models, the random effects of herd and boar within herd were included. No significant effect of system on volume of the ejaculate and total sperm production (TSP) was found, but there was a significant effect of month, age of the boar and collection interval on both volume and TSP (P<0.001). The interaction between system and month was significant (P<0.001). Temperature had a significant effect on volume in both systems (P < 0.01), and on TSP in the CONV system (P < 0.001) and in the EVAP system (P < 0.05). Humidity had a significant effect on both volume and TSP (P < 0.001) in the EVAP system. Volume and TSP decreased when temperature and humidity exceeded 30 degrees C and 40%, respectively, in the CONV system (P < 0.05), and 27 degrees C and 70%, respectively, in the EVAP system (P < 0.01). In conclusion, this study showed a seasonal variation in sperm production, and minor differences in the seasonal pattern were found between the two housing systems. High temperature and high humidity had negative effects on sperm production. The EVAP system might be one alternative way to reduce the seasonal variation in sperm production. (c) 2004 Elsevier B.V. All rights reserved.