EFFECT OF HOT SEASON ON LIVE SPERMATOZOA WITH INTACT ACROSOME IN HOLSTEIN BULLS

Semen characteristics were examined to find the deterioration of the percentage of live spermatozoa with intact acrosome during hot season using 5 Holstein bulls located in Shirnizu-cho Hokkaido Japan. Spermatozoal viability and acrosomal status were observed simultaneously with triple-stain technique for each spermatozoon. Spermatozoa were divided in four categories (live spermatozoa with intact acrosome, live spermatozoa without intact acrosome, dead spermatozoa with intact acrosome and dead spermatozoa without intact acrosome). Bull and collection month had significant effects on semen characteristics (p < 0.01). The percentage of live spermatozoa with intact acrosome and the percentage of live spermatozoa had the lowest least squares mean by collection month in August (72.7% and 76.7%). These two characteristics indicated the obvious deterioration during hot season. But the fluctuation of these two characteristics were not parallel and the differences between the two characteristics were largest during July to September. The present results indicate the necessity for the simultaneous determination of viability and acrosomal status of each Holstein bull's spermatozoa in order to keep fertility above an acceptable minimum level during hot season.