Variation in the timing of multiple ovulations following gonadotropin releasing hormone treatment and its relevance to collecting pronuclear embryos of sheep.
Timing of superovulation was examined by repeated laparoscopy in two Merino flocks treated with either pregnant mare serum gonadotropin (PMSG) plus gonadotropin releasing hormone (GnRH) or follicle stimulating hormone (FSH) plus GnRH. Observations were made in May (late breeding season), August (early anoestrous season), November (late anoestrous season), and February (midbreeding season). Data examined were time to first ovulation, time to all ovulations, and time from first to last ovulation. A GnRH-induced synchrony in the timing of superovulation occurred in Flock 1 irrespective of the month of observation. Approximately 80% of ovulations were recorded within 3 h with the median ovulation occurring 47 to 49 h after progestagen treatment. A similar synchrony was observed in Flock 2 in November and February. However, in May and August, the timing was asynchronous with some ewes superovulating as early as 10 or more hours before the median time obtained in November and February. An examination of this phenomenon indicated that 1) it also occurred when GnRH was not included in the treatment protocol, 2) it occurred irrespective of when ewes were exposed to vasectomized rams, and 3) it was more common in anovular ewes induced to superovulate than in spontaneously cyclic ewes. We concluded that treatment protocols developed for the collection of pronuclear embryos in Merino ewes during the breeding season can be less reliable when used out of season, thus increasing the possibility of collecting two- to four-cell embryos.
Walker
S K
SK
Department of Obstetrics and Gynaecology, University of Adelaide, Box 498, GPO Adelaide, South Australia, 5001, Australia.
Smith
D H
DH
Seamark
R F
RF
Godfrey
B
B