Relationships between antral follicle count and reproductive characteristics of embryo-recipient mares.

This research paper studies the relationship between the antral follicle count in mares and their ability to successfully carry a transferred embryo to term. The mares with a lower follicle count demonstrated a higher conception rate, especially in those that were currently in their reproductive cycle.

Methods

• Seventy-seven mares were evaluated based on their antral follicle count (AFC) and subsequently selected as potential carriers for embryo transfer.
• Embryos were transferred to the mares during specific periods, depending on their reproductive cycle. Cyclic recipients received embryos between days 4-6 after ovulation, while acyclic recipients received hormonal treatments to emulate a reproductive cycle.
• An intramuscular protocol was established for acyclic recipients that involved measured doses of estradiol benzoate (EB) and progesterone (P4).

Measurements and Analysis

• On the day of embryo transfer, the researchers carried out a number of measurements including the AFC, the mares’ weight, their body condition score (BCS), the diameter of the corpus luteum, their age, and the degree of uterine edema (UE).
• Pregnancy was confirmed at twelve and thirty days following the procedure.
• Mares with an AFC of eleven or less were categorized as holding a ‘low’ AFC, while those with more than eleven were determined to have a ‘high’ AFC.
• These data were comprehensively analyzed to identify patterns and correlations.

Results

• The degree of uterine edema (UE) was found to be influenced by the mares’ reproductive seasonality. Anestrus or non-cycling mares demonstrated higher levels of UE.
• Recipients with a low follicle count demonstrated a higher conception rate as compared to the high AFC group.
• Mares in their reproductive cycle also proved to have a higher conception rate than anestrus mares.
• The researchers discovered a potential link between AFC, reproductive seasonality, and conception rate. The highest conception rates were found in cyclic mares with a low follicle count, while the lowest rates were seen in anestrus mares with a high follicle count.

Conclusions

• The study concluded that mares demonstrating a lower antral follicle count have a higher conception rate when the embryo transfer occurs during the mare’s reproductive cycle.
• Additionally, the research suggests that the degree of uterine edema is influenced by the mare’s reproductive seasonality, with higher levels observed in non-cycling mares.