Superovulatory response to a single injection of PMSG (300ui) and of oFSH (3.6mg Ovagen®) given at either day 11, 16 or 18 after ovulation and a 7 day CIDR-G® or 30mg FGA sponge treatment was studied in Merino ewes. Follicle populations just before the administration of exogenous gonadotrophin and total ovarian response to treatment at day 5 of the next cycle were determined using transrectal ultrasound and laparoscopy respectively. The stage of the cycle had no significant effect on follicle population at the time of superovulation treatment or superovulatory response. Compared to FGA sponges, CIDR-G treatment reduced the number of 4-5mm follicles (2.83 ± 0.89 vs. 1.0 ± 0.3, P<0.05), the incidence of ewes with follicles ≥4mm (100% vs. 50%, P<0.05) and tended to increase superovulatory response (6.3 ± 3.7 vs. 10.3 ± 3.5, P<0.1). Ewes were classified according to the absence (n=4) and the presence (n=17) of a large follicle (>/=4mm diameter) at the time of superovulation treatment. Ewes without a large follicle had higher superovulatory response (13.8 ± 2.7 vs. 5.0 ± 1.3, P<0.05) and tended to have lower numbers of anovulatory follicles (0.5 ± 0.7 vs. 1.8 ± 0.3, P<0.1). These results suggest that the presence of a large follicle at the time of exogenous gonadotrophin treatment reduces superovulatory response in ewes and that the incidence of such follicles may be reduced by the use of a 7 day CIDR-G treatment.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 252-255, 1997
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