Seasonal variations in the incidence of sperm morphological abnormalities in dairy bulls regularly used for artificial insemination

Abstract

Nineteen dairy bulls aged between 1 1 2 years to 8 1 2 years were used to study the influence of season on bovine sperm morphology. The bulls were sampled during the winter, summer, spring and autumn of 1977 in the Northern United States of America where it was cold for most part of the year except summer. The winter temperatures (lowest) ranged from 5 °C to −30 °C, while the summer temperatures (highest) ranged from 21 °C to 43 °C. The incidence of sperm head abnormalities ranged between a mean of 1·34% in spring and 3·72% in summer, and there was significant seasonal variation ( p < 0·04). For proximal droplets, values ranged between a mean of 1·96% in winter and 3·08% in summer, and seasonal variation was also significant ( p < 0·02). There was no significant seasonal variation for distal droplets which ranged from a mean of 1·54% in winter to 2·33% in spring. Tail abnormalities for the four seasons were not significantly different: their range was between a mean of 2·91% in spring and 4·60% in summer. Tail-less heads ranged from a mean of 0·84% in the autumn to 2·74% in winter; there was no significant seasonal variation. Total abnormalities ranged between a mean of 11·21% in the autumn to 14·84% in summer. Seasonal variation for total abnormalities was significant ( p < 0·04). Summer was the hottest season of the year and in most of the bulls there were more proximal droplets, abnormal tails, abnormal sperm heads and total sperm morphological abnormalities during this season than during winter, spring or autumn. Manifestation of seasonal variation in the incidence of sperm morphological abnormalities was marked in most bulls, with peak values occurring during the summer.