Use of gonadotropin-releasing hormone, estrogen, or a combination to increase releasable pituitary luteinizing hormone in early transitional mares.

The research investigates the effects of different hormone treatments on the release of luteinising hormone (LH) in early transitional mares, particularly focusing on Gonadotropin-Releasing Hormone (GnRH), estrogen, or a combination of the two.

Background Information

• The study is driven by the idea that a lapse in pituitary LH stocks plays a role in seasonal anestrus and lack of ovulation during spring transition periods in mares.
• The experiment uses 40 mares and tests the effects of GnRH, estrogen, and a combination of the two on the ability of the pituitary gland to release LH.
• The mares in the experiment were classified based on their capacity to secrete LH upon a 950-micrograms GnRH challenge. They were then divided into four treatment groups: control mares without treatment, mares with daily estradiol-17 beta injections, mares with twice-daily injections of a GnRH analogue, and mares that first received estradiol treatments and then a combination of estradiol and GnRH.

Methodolody and Results

• Blood samples were taken on specific treatment days, and serum was analyzed for LH levels. Ten days post-treatment initiation, the mares were subjected to another GnRH challenge and had blood drawn for the next four hours.
• The findings showed that LH levels were fairly consistent across treatment days for the control group, estrogen-alone treated, and combination-treated mares.
• However, mares treated with GnRH alone had noticeably increased LH concentrations on treatment days 5 and 7.
• The response to the GnRH challenge, measured by the LH curve’s area and peak LH response, was significantly higher for the mares treated with GnRH alone or in combination with estradiol than for mares treated with estradiol alone or given no treatment.

Key Findings

• The results imply that GnRH treatment, with or without supplementary estrogen treatment, can significantly increase the LH levels and the pituitary gland’s LH release response to a GnRH challenge.
• The findings suggest that GnRH plays a critical role in stimulating LH release from the pituitary gland during the early transitional period in mares, and that estrogen alone may not be as effective.
• The implications of these findings could be significant for the management of equine reproductive health, particularly in understanding and potentially improving fertility during transitional periods.