Abstract: 73

TIMING OF THE LH SURGE AND OVULATION FOLLOWING GnRH ADMINISTRATION IN PYGMY GOATS.

J. T. Pierson¹ , H. Baldassarre² , C. L. Keefer^{2 *}, B. R. Downey^{1 *}
Department of Animal Science, Macdonald Campus, McGill University, Ste. Anne de Bellevue, Qc., Canada ¹
Nexia Biotechnologies Inc., Ste. Anne de Bellevue, Qc., Canada ²

Information on the temporal relationship among estrus, the LH surge, and ovulation in Pygmy goats is limited. This experiment was designed to measure these parameters, and to determine if gonadotropin releasing hormone (GnRH) improves their synchrony. Twelve Pygmy goats were synchronized during the breeding season with a 10–day progestagen sponge, 125 µg cloprostenol i.m. 48 h before sponge removal, and 300 i.u. pregnant mare serum gonadotropin (PMSG) IM at sponge removal. Six of the 12 goats were given 50 µg GnRH i.m. 24 h after sponge removal. Onset of estrus was monitored using two vasectomized males from 22 h, and plasma samples for luteinizing hormone (LH) were collected at 2–h intervals from 22 to 48 h after sponge removal. Ovulation time was confirmed by laparoscopy at 36, 50, 60, and 74 h. Estrus was induced in 5 of 6 GnRH–treated goats at a mean time of 25.8 ± 1.36 h , and in 3 of 6 control goats at a mean time of 30.0 ± 1.15 h after sponge removal. GnRH administration reduced the interval from sponge removal to the LH surge and the variability among animals (P<0.05). An LH surge was recorded in all GnRH–treated animals at a mean time of 26.0 ± 0.52 h, while three of the control goats had an LH surge at a mean time of 40.0 ± 1.63 h after sponge removal. Ovulation was observed in 5 of 6 GnRH–treated goats, three between 36 and 50 h and two between 50 and 60 h. Two control goats ovulated, one between 36 and 50 h and one between 50 and 60 h after sponge removal. These results show that GnRH reduces the time to the LH peak, and improves its synchrony. Further investigations with larger numbers are required to prove the hypothesis that GnRH improves the synchrony of ovulation. (Supported by CORPAQ)

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.