Luteal Tissue Area and Immunoreactive Concentration of Progesterone in Plasma of Bred and Non-bred Mares.

This research investigated the progesterone concentration and luteal tissue area in horses that were bred and became pregnant, compared to those that were bred and did not conceive, and those that were not bred at all. The study found no significant differences between these groups, suggesting that horse seminal plasma does not impact luteal function.

Objective of the Study

• The main goal of this study was to examine the progesterone concentration and luteal tissue area in different categories of mares: those that were bred and became pregnant, those that were bred but failed to conceive, and those that were not bred.
• The researchers hypothesized that mares that became pregnant would have higher progesterone concentrations than those that did not conceive.

Methods of the Study

• Researchers evaluated 52 cycles of mares (14 in total) using ultrasonography until a pre-ovulatory follicle was detected. Then, deslorelin acetate was administered to induce ovulation. After 24 hours, mares were either bred (using around 2 billion progressively motile sperm extended in 50 mL) or sham-bred (50 mL of extender).
• Ovulation was confirmed, and the number of corpora lutea and the luteal tissue area were recorded daily until 10 days post-ovulation. Progesterone concentration from the day of ovulation until 10-days post-ovulation was assessed daily.
• Pregnancy diagnosis was carried out at 10- and 13-days post-ovulation.

Study Results

• The data showed that progesterone concentration and luteal tissue area varied with time, but not significantly between groups. The study also found that multiple ovulations were associated with greater progesterone concentration and luteal tissue area.
• The observations suggested that horse seminal plasma does not affect luteal function in mares, given the lack of change in progesterone concentration and luteal tissue area between bred and non-bred mares.

Implications and Conclusions

• It was noted that all the mares had a progesterone level above 4 ng/mL after 5-days post-ovulation, indicating that if the study had included mares with abnormal progesterone concentration, the results might have been different.
• In conclusion, the study found that pregnancy was not associated with a higher progesterone concentration or larger luteal tissue area, debunking the initial hypothesis made by the researchers.