Reducing the examination interval to detect ovulation below 12 h does not improve pregnancy rates after postovulatory insemination with frozen/thawed semen in mares

Data were analysed retrospectively from fourteen breeding seasons at an Equine Fertility Clinic for the effect of interval between pre- and postovulatory examinations for immediate postovulatory insemination on pregnancy rate (PR) and embryo loss rate (ELR). Mares of various breeds and ages were examined at intervals which varied from 0.5 to 15 h between the pre- and postovulatory period over 867 cycles. When ovulation was detected they were inseminated with a single dose of commercial frozen–thawed semen. All mares were treated in the post-insemination period with intrauterine antibiotics and then with oxytocin. Pregnancy diagnoses were made at 12–17 days post-ovulation and at intervals up to 40 days. The overall PR was 47.9%. The data were pooled into 3 h examination intervals. In the first interval, mares were inseminated at the time of ovulation to 3 h post-ovulation (n = 44) with a PR of 43.2%. Results of insemination to consecutive 3 h intervals gave PR of 44.7% (3–6 h, n = 150), 45.1% (6–9 h, n = 432), 55.8% (9–12 h, n = 190) and 54.9% (12–15 h, n = 51). ELR was 10.5%, 11.9%, 5.6%, 7.5% and 3.6% respectively for the same intervals. There was no statistical difference in either the PR or ELR. It is concluded that in a postovulatory insemination regime with routine post-insemination treatment as described, examination of mares at intervals of any less than 12–15 h does not improve pregnancy or embryo loss rates.