The effect of time of insemination with fresh cooled transported semen and natural mating relative to ovulation on pregnancy and embryo loss rates in the mare.

ABSTRACT

One hundred and fifty-four mares were inseminated with fresh semen either during the pre- or post-ovulatory periods at different intervals relative to ovulation 36-24 h (n = 17) and 24-0 h (n = 30) before ovulation; 0-8 h (n = 21), 8-16 h (n = 24), 16-24 h (n = 48) and 24-32 h (n = 14) h after ovulation. All mares received the same routine post-mating treatment consisting of an intrauterine infusion with 1 litre of saline and antibiotics followed 8 h later by an intravenous administration of oxytocin. Artificial inseminations (AI) from 36 h before ovulation up to 16 h post-ovulation were performed with transported cooled semen. While there was no data available for inseminations later than 16 h, data from natural mating after 16 h post-ovulation were included. Pregnancy rate (PR) of mares inseminated 36-24 h (29.4%) was significantly lower (p < 0.05) than mares inseminated 24-0 h before ovulation (60%), 0-8 h (66.7%) and 8-16 h (70.1%) post-ovulation. Embryo loss rate (ELR) was highest in mares mated 24-32 h after ovulation (75%). PR of mares mated 16-24 h post-ovulation (54.1%) did not differ significantly from any other group (p > 0.05); however, the ELR did increased markedly (34.6%) compared with inseminations before 16 h post-ovulation (<12%). At ≥ 30 days post-ovulation, PR of mares mated 16-24 h after ovulation (35.4%) was significantly lower than mares mated 0-16 h after ovulation (62%). Good PR with acceptable ELR can result from inseminations within 16 h of ovulation, at least with this specific post-mating routine treatment.