Luteinizing hormone during sexual maturation in pony mares

Area of Science:

• Reproductive endocrinology
• Equine science
• Veterinary medicine

Background:

• Sexual maturation in pony mares involves complex hormonal changes and ovarian follicular development.
• Luteinizing hormone (LH) plays a critical role in ovulation, but its precise role in the initial stages of sexual maturation is less understood.
• Understanding the hormonal dynamics during sexual maturation is crucial for reproductive management in horses.

Purpose of the Study:

• To quantify luteinizing hormone (LH) concentrations in pony mares during artificially induced sexual maturation.
• To assess ovarian follicular development alongside LH quantification.
• To investigate the temporal relationship between follicular development and LH surges associated with ovulation.

Main Methods:

• Luteinizing hormone (LH) levels were measured in pony mares undergoing induced sexual maturation.
• Ovarian follicular development was monitored using rectal palpation.
• LH concentrations were compared between mares showing sexual maturation and those that were not.

Main Results:

• LH concentrations were not significantly different between mares with and without marked follicular development.
• An exception was observed in two mares with large periovulatory LH concentrations that ovulated.
• These findings indicate a dissociation between the onset of follicular development and the ovulatory LH surge.

Conclusions:

• The initial phase of follicular development in pony mares occurs independently of significant changes in baseline LH levels.
• A distinct temporal separation exists between the initiation of follicular growth and the LH surge that triggers the first ovulation of the year.
• This dissociation highlights a nuanced hormonal control of equine reproductive cycles.