EFFECT OF TIMING OF FROZEN-SEMEN INSEMINATION ON PREGNANCY RATE IN MARES

Thirty-four mares were inseminated with frozen semen from one stallion during 2 oestrous cycles, every 48 h until ovulation took place and w ithin 12 h after ovulation. Semen was frozen using the Colorado method . The insemination dose was from 200 to 400x10(6) progressively motile spermatozoa. Ovaries were examined every 12 h to determine time of ov ulation. Examination for pregnancy was carried out using ultrasonograp hy, 15 days after ovulation. Thirty-five per cent of mares inseminated < 24 h and 23% of mares inseminated between 24 - 48 h before ovulatio n were pregnant (p = 0.388). The pregnancy rate in all mares inseminat ed before ovulation was 30%. In the mares inseminated within 12 h of o vulation, it was 18% (p = 0.253). Younger mares (aged 4-10 yr) had a h igher pregnancy rate (59%) than older mares (aged 11-15 yr) (23%), but the difference was not statistically significant (p = 0.057).