Ovarian activity in progesterone treated mares following administration of pregnant mare serum gonadotropin.

Twelve non-pregnant, non-lactating mares were randomly assigned to four treatment groups using a 2x2 factorial arrangement with three replicates per group. Mares were administered PGF(2alpha) (10 mg, IM) on days -14 and 0, followed by HCG (3000 IU, IM) on day 5. The following treatments were administered: Group A received PMSG on days 2 (4000 IU, IM) and 5 (1000 IU, IV); Group B received PMSG (4000 IU, IM) on day 2; Group C received PMSG (1000 IU, IV) on day; Group D received no PMSG. Mares received progesterone (25 mg, IM) on days 1 through 4. Reproductive tracts were recovered at necropsy on day 16 (10 days post-ovulation). Ovaries were weighed, CL number and weight determined, follicles counted and measured, and volume of follicular fluid quantified. Mean ovarian weight (g) and number of CL per mare, respectively were: Group A, 100.0+/-15.6, 1.7+/-.7; Group B, 128.6+/-40.4, 1.3+/-.7; Group C, 92.4+/-21.0, 2.0+/-.0; Group D, 93.3+/-12.3; .3+/-.3. Mean number of follicles >10 mm and total volume (ml) of follicular fluid per mare, respectively, were: Group A, 9.4+/-2.0, 21.8+/-10.9; Group B, 1.3+/-.3, 32.2+/-28.9; Group C, 4.3+/-1.8, 5.4+/-2.3; Group D, 6.0+/-4.5, 24.0+/-10.3. There was no difference (P>.05) in mean ovarian weight, CL number, CL weight, follicular fluid volume, number of follicles, or size of follicles between treatment groups. These results show no significant effect on ovarian activity in progesterone treated mares following administration of exogenous PMSG.