Effect of various doses of a gonadotropin-releasing hormone analogue on induction of ovulation in anestrous mares.

The research article explores the effects of different doses of goserelin acetate, a gonadotropin-releasing hormone (GnRH) analogue, on inducing ovarian cyclicity in anestrous mares. The study observed variations in follicular activity, progesterone and LH concentrations, and differential ovulation rates based on GnRH dosage and follicle size.

Objective of the Research

• The primary aim of the study was to investigate how different doses of a GnRH analogue, goserelin acetate, would affect the induction of ovulation in “off-season” or anestrous mares.
• This research sought to understand the relation of various doses on follicular activity, luteinizing hormone (LH), and progesterone levels, and how these factors influenced ovulation.

Methodology

• Study involved 100 anestrous mares in early February and they were injected with implants containing 0, .9, 1.8, 3.6, or 5.4 mg of goserelin acetate.
• Follicular activity and concentrations of progesterone and LH were determined every three days, or daily during estrus.
• The study compared the time to second ovulation of the season for treated mares that ovulated with another group receiving 16 hours per day of light beginning December 16 (positive controls).
• Mares that did not ovulate in 30 days were given an intravenous bolus of GnRH on day 33 or 34, and their hormone levels were monitored at multiple intervals.

Findings

• More mares ovulated when given 3.6- (n = 7) or 5.4-mg (n = 6) implants than when given .9-mg implants (n = 0) or placebo (n = 0).
• Mares with initial follicles < or = 15 mm in diameter were less (P < .05) likely to ovulate (10 of 88) than were those with follicles 16 to 20 mm in diameter (5 of 12).
• The area under the curve (AUC) for LH was greater for mares receiving larger doses of GnRH, indicating a direct correlation between the dose and LH production.
• There was no significant difference in either peak LH or AUC among treatment groups in response to the GnRH challenge, suggesting dose size did not materially alter the hormone’s effectiveness.