Control of onset of breeding season in the mare and its artificial regulation by progesterone treatment.

The article revolves around a study on mares to manipulate the onset of breeding season through progesterone treatment. However, the researchers discovered that the treatment does not consistently affect follicular development or advance the first ovulation of the season.

Research Objectives and Protocol

• The study aimed to understand the role of hormones in controlling the onset of breeding season in mares and the potential for its artificial regulation via progesterone treatment.
• 12 mares were meticulously monitored from their deepest period of anoestrus through to their first ovulation of the breeding season. This involved checking plasma LH and FSH levels and their pulse frequencies, along with the size of the largest ovarian follicle.
• Five of these 12 research mares, along with 20 other mares at a commercial stud farm, were subjected to daily intramuscular injections of 150 mg progesterone for 12 days. The treatment was done when their ovaries showed signs of containing developing follicles.

Observations and Results

• The researchers noticed that the mares’ high LH levels were closely tied to the time of ovulation. Conversely, FSH levels were significantly reduced in deep anoestrus and when a pre-ovulatory follicle was present.
• Despite the progesterone treatment, the size of the largest follicle did not differ from pre-treatment or control values. In simple terms, the mares’ follicular development was not significantly impacted by the treatment.
• Regarding ovulation, the research mares ovulated almost synchronously about 11.2 days post progesterone withdrawal. Contrarily, ovulation was not as synchronized in the commercial mares and took generally longer, approximately 23 days after progesterone withdrawal.
• The study found that progesterone treatment did not advance the mean date of first ovulation compared with untreated mares. This effect was consistent in both the research group and commercial mares.

Hormonal Levels and Pulse Frequencies

• Progesterone treatment neither affected the mean plasma LH levels nor significantly elevated the mean FSH levels in the research mares.
• In both control and treated commercial mares, mean FSH levels dropped over time.
• The only noticeable difference in LH and FSH pulse frequency between treated and control research mares surfaced post-progesterone withdrawal when the pulse frequency was higher in control mares.

Conclusion

• The study concludes that exogenous progesterone does not have a consistent effect on follicular development or gonadotrophin secretion patterns in mares during their transition phase towards the breeding season.
• Most notably, the treatment did not advance the mean date of the first ovulation of the breeding season when compared with untreated control mares.