Serum Progesterone and Conception Rates in Acyclic Embryo Recipient Mares Using a Bovine Progesterone-Releasing Intravaginal Device.

This research evaluates the impact of using a bovine progesterone-releasing intravaginal device on progesterone levels, uterine features, and pregnancy success in mares that are not currently in a reproductive cycle. The study concludes that this method sufficiently prepares the uterus for embryo transfer and yields similar conception rates to the standard protocol of using injectable progesterone.

Objective and Methodology of the Research

• The primary objective of this study was to examine the effects of a bovine progesterone-releasing intravaginal device on serum progesterone levels, the features of the uterus, and conception rates in mares that are acyclic, meaning they are not experiencing regular reproductive cycles.
• The researchers involved in this study used a total of 73 recipient mares aged between 3 and 10 years. The experimental animals, of unknown breed, weighed between 350 and 500 kg and were kept under an intensive management system. These mares had free access to water, Tifton 85 (Cynodon spp.) pastures, and mineral salt.
• The mares were split into two study groups: one that received a progesterone-releasing intravaginal device in which 1 g of progesterone was included (G-IVP4, n = 24), and a control group (G-iP4, n = 49) that received an injection of long-acting progesterone amounting to 1,500 mg.

Procedure and Measurements

• In the G-IVP4 group, jugular blood samples were collected on three distinct days: Day 0, when the intravaginal device was inserted; Day 5, the day of the embryo transfer; and Day 9, the day of pregnancy diagnosis, to measure progesterone levels via radioimmunoassay.

Results and Conclusion

• The researchers observed a significant increase (P < .0001) in serum progesterone levels on Day 5 and Day 9 as compared to Day 0 (4.09 ± 0.81 and 6.45 ± 1.03 ng/mL vs. 0.71 ± 0.14 ng/mL respectively).
• However, there were no significant differences (P > .05) in the pregnancy rate between the two groups, with rates of 83.33% for G-IVP4 and 73.46% for G-iP4, respectively.
• Based on these results, it was concluded that the intravaginal device, with an absorption rate of 1g of progesterone, appropriately increased progesterone serum levels to prepare acyclic recipient mare uteruses for embryo transfer. This method achieved a conception rate equivalent to the standard protocol that uses long-acting injectable progesterone.