THE EFFECT OF GNRH AGONIST (BUSERELIN) TREATMENT ON DAY 12 POST MATING ON THE REPRODUCTIVE-PERFORMANCE OF EWES

An investigation was conducted to determine the effects of treatment w ith the GnRH agonist buserelin on day 12 post mating on the reproducti ve performance of ewes. There was a non-significant (P > 0.05) increas e in non-return rate (control 0.76 v. buserelin 0.83) and litter size (control 1.51 v. buserelin 1.77) in three flocks. However, there was a significant (P < 0.05) increase in the number of twin lambs born (con trol 20 v. buserelin 40) and litter size (control 1.44 v. buserelin 1. 68) in the yearling flock. There was no effect of buserelin on oestrou s cycle length, although there was a tendency for treated animals to h ave a longer gestation length and heavier lambs. In a ewe lamb flock t here was no effect of buserelin on non-return rate or litter size asse ssed post slaughter on day 31 of pregnancy. However, ovulation rate te nded to be greater in the treated animals, which suggests that buserel in may have induced the formation of accessory corpora lutea. These re sults indicate that buserelin treatment improves embryo survival and t hat this effect is particularly evident in yearling ewes.