The largest and most well-endowed male sheep can copulate as many as 13 times a day, but in the end they can't compete with their smaller counterparts, according to a report in the 8 February Nature . Towards the end of the breeding season it is the smaller males who, having exerted themselves less, sire more lambs. The scientists also found an effect of copulation frequency on sperm quality. Rams that copulate more frequently produce fewer healthy sperm at the end of the breeding season. It seems too much sex can have ram-ifications.
Dominant rams lose out by sperm depletion.