Sexual behaviour and semen characteristics of boars: effects of high temperature

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Abstract
The effect of 4, 7 or 10 day periods of high air temperatures on the sexual behavior and semen characteristics of mature Large White crossbred boars was determined in 3 experiments. In experiment 1, boars kept at 40.degree. C for 8 h and 30.degree. C for 16 h each day for 7 days had lower courting behavior activity when tested at 40.degree. C than control boars tested at < 25.degree. C. After similar heat treatment in experiment 2, boars tested at 30.degree. C showed no significant differences in courting or copulatory behavior from control boars, but the semen of 2 of 6 treated boars showed evidence of severe testicular-epididymal dysfunction. The semen of a 3rd treated boar showed evidence of moderate testicular-epididymal dysfunction. In experiment 3, 4 boars were given a similar daily high temperature cycle to the above, either for 4 or 10 days. Two of the 4 boars given high temperatures for 10 days had semen with signs of severe testicular-epididymal dysfunction. The semen of the other 2 boars in this group and 1 boar treated for 4 days, showed evidence of moderate dysfunction. During hot weather boars will mate normally during the cooler part of the day and they are able to tolerate short periods of heat stress (< 4 days) without detriment to semen characteristics. Protection from longer periods of high temperatures (> 7 days) is necessary.