Pharmacologic application of native GnRH in the winter anovulatory mare, I: frequency of reversion to the anovulatory state following ovulation induction and cessation of treatment.
Abstract: The continuous, subcutaneous infusion of native GnRH into seasonally anovulatory mares stimulates the synthesis and secretion of LH without pituitary refractoriness, offering opportunities to markedly accelerate the timing of ovulation within the operational breeding season. Herein, we tested the hypothesis that ovarian cycles induced in winter anovulatory mares using continuous administration of native GnRH for 28 days, beginning in either early February or early March (North America) would not revert to an anovulatory state after treatment withdrawal. Anovulatory mares received sham pumps (control) or native GnRH (100 μg/h) for 28 days beginning from February 2 or 3 (GnRH-Feb) or March 2 or 3 (GnRH-Mar). Mean concentrations of LH were five- to seven-fold greater during February in the GnRH-Feb group compared with control and GnRH-Mar groups through February and ending on March 2 or 3. However, concentrations of LH returned to the winter baseline within 3 to 11 days after pump removal and all GnRH-Feb mares failed to remain cyclic after treatment withdrawal. Correspondingly, during March, concentrations of LH in the GnRH-Mar group were greater (P < 0.001) than in the control and GnRH-Feb groups during the 28-day treatment period. Follicular growth and frequency of ovulation (6/10 GnRH-Feb; 9/10 GnRH-Mar, 1/11 controls, respectively) were greater (P < 0.01) in GnRH-treated mares. Ovulatory cycles continued in five of nine GnRH-Mar mares that ovulated, with interovulatory intervals of 15 to 24 days; whereas, three of nine mares had extended (33-42 days) interovulatory intervals and one of nine mares had a persistent CL after cessation of treatment. In summary, continuous administration of native GnRH for 28 days, beginning in early February or March, elevated circulating LH adequately to stimulate follicular growth and ovulation up to 60 days earlier than in untreated controls. However, if continuous, subcutaneous infusion of GnRH is selected as the only pharmacologic or managerial intervention, and mares are not pregnant, treatment must be continued at least until the end of March. This will improve the likelihood of a normal interovulatory interval after treatment withdrawal.
Copyright © 2014 Elsevier Inc. All rights reserved.
Publication Date: 2013-12-08 PubMed ID: 24411221DOI: 10.1016/j.theriogenology.2013.11.018Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research explores the impact of administering native Gonadotropin-Releasing Hormone (GnRH) to winter anovulatory mares to stimulate ovulation, and its continuity after the treatment cessation. The findings showed that while the treatment can enhance ovulation, its effects cease soon after the treatment is withdrawn.
Introduction and Methodology
- The research postulates that using continuous administration of native GnRH can induce ovulatory cycles in winter anovulatory mares (mares that do not ovulate during winter). This was tested over a period of 28 days, starting from early February or March.
- The test groups were anovulatory mares that received infusion of native GnRH (100 μg/h) for 28 days beginning from either February (GnRH-Feb group) or March (GnRH-Mar group).
- The control group consisted of mares that received sham pumps.
Results and Findings
- Luteinizing hormone (LH) concentrations were significantly higher (five- to seven-fold) in February in the GnRH-Feb group compared to the control and GnRH-Mar groups. However, the LH concentration returned to winter baseline levels within 3 to 11 days after pump removal. Moreover, all mares in the GnRH-Feb group failed to maintain the ovulation cycle after the treatment ceased.
- In March, the LH concentration in the GnRH-Mar group was significantly higher than in control and GnRH-Feb groups, during the 28-day treatment period.
- Induction of follicular growth and ovulation was significantly higher in GnRH-treated mares. Out of these, six out of ten mares in the GnRH-Feb group and nine out of ten mares in GnRH-Mar group ovulated successfully, as compared to only one out of eleven in the control group.
- Out of the nine ovulating mares in the GnRH-Mar group, five continued to have ovulatory cycles with interovulatory intervals of 15 to 24 days; three had extended interovulatory intervals of 33 to 42 days, and one had a persistent corpora lutea after treatment cessation.
Conclusions
- Continuous administration of native GnRH successfully raised LH levels, thus stimulating follicular growth and ovulation.
- However, discontinuation of the treatment led to an immediate drop in LH levels and cessation of the induced ovulatory cycles. This suggests that the treatment needs to continue at least until the end of March to ensure continuity of ovulation after withdrawal.
Cite This Article
APA
Thorson JF, Allen CC, Amstalden M, Williams GL.
(2013).
Pharmacologic application of native GnRH in the winter anovulatory mare, I: frequency of reversion to the anovulatory state following ovulation induction and cessation of treatment.
Theriogenology, 81(4), 579-586.
https://doi.org/10.1016/j.theriogenology.2013.11.018 Publication
Researcher Affiliations
- Animal Reproduction Laboratory, Texas A&M AgriLife Research, Beeville, Texas, USA; Department of Animal Science, Texas A&M University, College Station, Texas, USA.
- Animal Reproduction Laboratory, Texas A&M AgriLife Research, Beeville, Texas, USA; Department of Animal Science, Texas A&M University, College Station, Texas, USA.
- Department of Animal Science, Texas A&M University, College Station, Texas, USA.
- Animal Reproduction Laboratory, Texas A&M AgriLife Research, Beeville, Texas, USA; Department of Animal Science, Texas A&M University, College Station, Texas, USA. Electronic address: glwilliams@tamu.edu.
MeSH Terms
- Anestrus / drug effects
- Anestrus / physiology
- Animals
- Female
- Gonadotropin-Releasing Hormone / administration & dosage
- Gonadotropin-Releasing Hormone / pharmacology
- Horses / physiology
- Luteinizing Hormone / blood
- North America
- Ovarian Follicle / diagnostic imaging
- Ovarian Follicle / physiology
- Ovulation Induction / veterinary
- Seasons
- Ultrasonography
Citations
This article has been cited 1 times.- Guo HX, Yuan B, Su MT, Zheng Y, Zhang JY, Han DX, Wang HQ, Huang YJ, Jiang H, Zhang JB. Identification of Circular RNAs in the Anterior Pituitary in Rats Treated with GnRH. Animals (Basel) 2021 Aug 31;11(9).
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