The relation of semen and vaginal mucus traits to fertility in the Australian Merino

Abstract

Data relating semen traits and vaginal mucus scores in 515 ram years and 4190 first inseminations to subsequent lambing performance of ewes were analysed by a range of statistical methods. The results showed there to be an important curvilinear effect of mucus score at insemination time and linear effects of scores for motility and consistency of semen in the ejaculates used. These effects operated both on fertility and on fecundity. There appeared also to be smaller linear effects of volume of semen inseminated per ewe and estimates of the proportion of abnormal spermatozoa in ejaculates collected before the insemination season on fecundity and probably on fertility. The effects of age of ewe on fecundity to a single insemination are in contrast with the usual effects of age on lambs born under natural mating. In our material two-tooth ewes produced 5–6% more lambs from a single insemination than did older ewes. It is suggested that, while older ewes are more sexually active and shed increased numbers of ova, the reproductive tract becomes a less favourable environment for initiation and completion of pregnancy with increasing age.