Frequency of semen collection in boars and quality of ejaculates as evaluated by the osmotic resistance of acrosomal membranes

Abstract

Semen was collected from five adult boars at 2-day intervals subsequent to a longer testing period with regular twice-weekly semen collections. After ten collections at 2-day intervals, the volumes of the ejaculates were reduced on average from 120 ml (ejaculates 1 and 2) to 86 ml (ejaculates 9 and 10), the sperm numbers from 35×10 9 to 16×10 9, motility from 78% to 63% and spermatozoa with normal acrosomal ridge (NAR) from 83% to 70%. The differences are statistically significant ( P<0.01). The differences in preserved semen samples from ejaculates 9 and 10, compared to samples from ejaculates 1 and 2 of this experiment, were even larger, with decreases in motility from 45% to 12% (frozen/thawed semen) and to 26% (72 h stored semen) and in NAR from 54% to 22% (frozen/thawed semen) and to 27% (stored semen). Such semen samples must be rejected and cannot be used for insemination. All five boars reacted similarly. Incubation of fresh samples from the beginning and from the end of the experiment in media with extreme osmolalities resulted in a dramatic decrease of % NAR in the latter. This demonstrates a reduced osmotic resistance in their acrosomal membranes, probably as a consequence of a shortened maturation of the spermatozoa in the epididymis due to frequent ejaculations. The determination of the osmotic resistance value (ORT) in fresh semen samples permits a quantitative and continuous control of semen quality and of overuse of boars by frequent semen collecting systems.