An assessment of sperm motility estimation for evaluation in rams

There is disagreement about the value of estimating spermatozoal motility as a predictor of fertility in rams. We tested the hypothesis that sperm motility can help one to predict lambing rate by evaluating sperm motility in rams prior to breeding and by subsequently breeding the rams regardless of their sperm motility results. A total of 943 rams (Merino, n=630 and Romney Marsh, n=313) was used during two breeding seasons. For fertility evaluation only 804 rams that bred at least ten ewes each were included in the study. Rams were grouped into 4 groups according to sperm motility scores, ranging from the lowest, which included rams with azoospermia, oligospermia, non-motile and single-motile sperm, through rams with 10 to 30%, 30 to 60%, to the highest at 60 to 100% motile sperm. The corresponding fertility rates found in our study in Merino and Romney breeds were 58.3 and 47.4%, 75.1 and 59.1%, 79.4 and 64.1% and 81.5 and 64.0%, respectively. We concluded that there was a statistically confirmed difference in fertility between the lowest and all the other motility categories. The differences in fertility among rams that had motility categories above 10% were not statistically significant. Evaluation of breeding soundness in large scale surveys of rams, based on sperm motility estimation, may be misleading. Clinical examination of genital organs seems to offer a reliable source of information about rams, and may be considered adequate in sheep breeding.