Influence of age and ovarian antral follicle count on the reproductive characteristics of embryo donor mares.

This study analyzes the effect of a horse’s age and count of small, fluid-filled sacs in the ovaries known as antral follicles (AFC), on their reproductive characteristics. It suggests that younger mares with more of these follicles experience faster follicular growth and higher uterine oedema but that these factors don’t impact the rate of embryonic development.

Study Scope and Methodology

• The focus of this research was to explore the impact of a mare’s age and antral follicle count (AFC) on reproductive characteristics. While data about this connection exists for cattle, it remains scarce for horses.
• The study involved 15 Quarter Horse mares aged from three to 17 years, with an AFC ranging from 5 to 15. These horses were divided into different groups based on age (young or old) and AFC (low or high).
• All mares were monitored for at least three estrous cycles, using ultrasonography to determine various metrics such as the dominant follicle diameter, follicular growth rate, degree of uterine oedema (fluid accumulation within the uterus), and embryonic recovery.

Findings and Results

• According to the findings, younger mares had a higher AFC compared to older mares.
• There was a significant interaction between AFC and age in terms of follicular growth rate. Specifically, older mares with a low AFC had slower follicular growth in comparison to the other groups (low AFC and young, high AFC and old, and high AFC and young).
• On the third day of the estrous cycle, younger mares and those with a high AFC had a higher degree of uterine oedema relative to older mares or those with a low AFC. However, the degree of oedema was reduced by the time of ovulation, irrespective of the group.

Conclusions

• The rate of follicular growth, the degree of uterine oedema, and the number of antral follicles are higher in younger mares with a high AFC.
• Interestingly, irrespective of a mare’s age or AFC, the rate of embryonic recovery was constant. Indicating that while AFC and age can affect some reproductive characteristics, they do not impact the primary stage of embryonic development.