The Peripheral Levels of Luteinizing Hormone(LH), Follicle-Stimulating Hormone(FSH), Immunoreactive(ir-) Inhibin, Progesterone(P) and Estradiol-17.BETA.(E2) at the Time of Control of Ovulation With Gonadotropin Releasing Hormone(GnRH) Agonist(Deslorelin) in Pony Mares.

Abstract

Control of ovulation in mares obviously has many advantages in a breeding program. Two pony mares were challenged against synthetic Gonadotropin Releasing Hormone (GnRH) agonist (Deslorelin) for six consecutive cycles. Clinical and endocrinological findings after treatment (n=6) with GnRH agonist were compared with those of the control findings before treatment (n=3) of the same mares. The time interval from administration of the GnRH agonist till ovulation (43.5 ± 4.0 hr) and the length of the estrous cycle (19.5 ± 1.0 days) at the time of treatment were significantly (p<0.05) shortened as compared with those of the control. A preovulatory sharp rise in plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was also noticed 24 hr from the time of GnRH agonist injection and one day prior to ovulation in the studied mares, but there were no significant differences before and after treatment with GnRH agonist on the levels of ir-inhibin, progesterone (P) and estradiol-17 β (E2). It seems likely that GnRH agonist is beneficent in reducing the number of matings needed for conception in a natural mating program and that ovulation in mares may be induced by a sharp preovulatory rise in LH and FSH.