Influence of season, age, breed and some other factors on the variation in sperm morphological abnormalities in Swedish dairy A.I. bulls

Fifty-two dairy A.I. bulls aged from 14 months to 6 and a 12 years old were used to study the effects of age, breed, season and, dehorning and dihydrostreptomycin treatments on the incidence of sperm morphological abnormalities in fresh semen. The highest mean value of sperm abnormalities was recorded for abnormal heads (6.1%), but most of the recorded abnormalities only occurred in approximately 1–2% of the studied spermatozoa. Significant seasonal variation occurred in the incidences of sperm head abnormalities and total sperm abnormalities. Least-squares means for sperm abnormalities were significantly higher during the warmer seasons (spring, summer) compared with the colder ones (autumn, winter). The incidence of sperm abnormalities (abnormal heads, proximal droplets, total abnormalities) was relatively constant over time within bull (repeatability estimates varied between 0.36 and 0.54), but was significantly affected by age (abnormal heads and acrosomes, total abnormalities) and breed (abnormal heads, detached heads). The incidence of total sperm abnormalities was also found to be significantly increased in semen from a group of bulls submitted to both dehorning and double injections of dihydrostreptomycin (DHS) when comparing pre- and posttreatment periods. The results indicate that age, breed and seasonal effects as well as repeated stressful treatments influence the sperm characteristics and must be considered when evaluating bulls for sperm morphological traits.