Two experiments were conducted to compare PMSG injection to GnRH infusion for induction of breeding in anoestrous ewes. In Experiment One, sixteen Suffolk ewes were pre-treated for 14 days with 30 mg Cronolone sponges. At sponge removal half of the ewes received 0.125 ug/hr GnRH for 72 hours via subcutaneous osmotic pumps. The other half received a single injection of 750 iu PMSG. Plasma LH levels gradually increased and were sustained for 24 hours. Estrus, ovulation and corpus luteum function were expressed in half of the ewes treated with GnRH. All ewes treated with PMSG exhibited estrus, ovulated and formed functional corpora lutea. In Experiment Two, 24 ewes were divided into two groups and the same treatments as in Experiment One were applied. Fertile rams were introduced to all the ewes at the time of sponge removal. Estrus was detected in 75% of the GnRH treated ewes vs 100% in PMSG treated ewes. Lambing rates were 44% and 56% in GnRH and PMSG groups respectively. These results suggest that the induction of fertility using continuous infusion of GnRH is encouraging. However, other GnRH delivery systems should be investigated.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 427-430, 1990
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