Seasonal variation in semen characteristics and the fertility of finn cross rams subjected to frequent ejaculation

Abstract

Three Finn cross rams were put on a daily regime of five successive ejaculations for 17 consecutive days in June, August–September, November–December and March. The semen characteristics of the first and fifth ejaculates, and the fertility of the ewes receiving these ejaculates, were examined. Ewes were inseminated once, either naturally or artificially, 51–54 hours after the end of a hormone treatment for synchronization or induction of oestrus. The semen volume, sperm density, sperm number and the percentage of abnormal spermatozoa decreased from the first to the fifth ejaculate from 0.58 to 0.49 ml; 3.6 to 2.9 × 10 9; 2.2 to 1.5 × 10 9; and from 13.9% to 11.1%, respectively. A significant season × ejaculate interaction on sperm density and number was found. The sperm density, sperm number and percentage of abnormal spermatozoa also decreased in the course of the 17-day experimental periods (b = -0.058 × 10 9, −0.039 × 10 9, and −0.28%, respectively). The mean percentage of abnormal spermatozoa of the first and fifth ejaculates was higher in March (20.8%) than in June (7.1%), August–September (8.5) and November–December (13.5%). The fertility of the sperm, assessed by the lambing rates of the ewes, was not significantly different after artificial insemination (53.0%) from that obtained after natural service (61.7%); during the first days (45.0%) from that found during the last days (53.2%) of the 17-day experimental periods; and of the first ejaculate (54.4%) from the fertility of the fifth ejaculate (59.5%). A significant decrease was observed in sperm fertility in March (36% lambing rate vs 54–70% in the other seasons). It is concluded that an ejaculation frequency of five successive ejaculations for 17 consecutive days does not affect the fertility of Finn cross rams, irrespective of the season of semen collection.