The effect of hCG, GnRH and PGF2α analogue cloprostenol on the oestrus cycle in jennies

Abstract

The objectives of this study were twofold. Firstly, the present study was designed to examine susceptibility of the corpus luteum (CL) in early diestrus in jennies; and secondly, to investigate the effect of two commonly used hormonal agents in horses on the induction of ovulation in jennies. The oestrus cycles of eleven jennies were monitored by ultrasound every day. When the dominant follicle reached a diameter of 30 mm, the jennies were treated by intramuscular administration of gonadotropin-releasing hormone agonist lecirelin (GnRH, 50 µg pro toto) in the first oestrus cycle, and human chorionic gonadotropin (hCG, 1500 IU pro toto) intramuscularly in the second oestrus cycle. Prostaglandin F2α analogue cloprostenolum (PGF2α, 0.125 mg pro toto) was administered intramuscularly 2 days after the first ovulation and the interovulatory interval was monitored. This study showed that intramuscular administration of 50 µg of GnRH agonist lecirelin resulted in ovulation within 48 h in 73% of treated jennies. Intramuscular administration 1500 IU of hCG was found to be poorly effective to induce ovulation, with 36% of animals ovulating within 48 h. Intramuscular administration of PGF2α analogue cloprostenol 2 days after ovulation was unsuccessful in attempting to shorten the interovulatory interval in donkeys.

Hormonal Management for the Induction of Luteolysis and Ovulation in Andalusian Jennies: Effect on Reproductive Performance, Embryo Quality and Recovery Rate

“…There are several hormones that can be used to induce ovulation in equine species [ 30 , 31 ], such as human Chorionic Gonadotropin (hCG), Equine Pituitary Extract (EPE) and Gonadotropin-Releasing Hormone (GnRH). Although the efficacy of both EPE and GnRH in hastening ovulation has been widely proven in mares [ 26 , 28 , 30 , 32 , 33 , 34 ], hCG is still the most popular inductor, not only in mares [ 27 , 30 , 31 ], but also in jennies [ 35 , 36 ], due to its high efficacy, easier commercial availability and lower cost. However, various studies have shown that repeated administration of this hormone can stimulate the synthesis of anti-hCG antibodies, leading to a loss of its effectiveness [ 37 , 38 ].…”