The effect of exogenous estradiol benzoate and altrenogest on uterine and ovarian blood flow during the estrous cycle in mares.

This research article explores the impact of exogenous estrogen and progestin on uterine and ovarian blood flow in mares. The study discovered that these exogenous hormones decreased genital perfusion in cycling mares.

Study Design and Procedure

• The researchers used five Trotter mares for the study, examining them every day during three of their estrous cycles.
• The mares were assigned to three different treatment groups: non-treated, altrenogest-treated (from ovulation until Day 14) and estradiol benzoate-treated (Days 0, 5, and 10).
• Transrectal Doppler sonography—a non-invasive technique that allows the assessment of blood flow—was used to monitor blood flow in both the uterine and ovarian arteries.
• During estrus, the ovarian artery blood flow paired with the preovulatory follicle was analysed, and during diestrus, the blood flow paired with the corpus luteum was examined.
• Blood flow was assessed using the pulsatility index (PI), where high PI values indicate high resistance and low perfusion, and vice versa.

Analyzing the Effects of Exogenous Estrogen and Progestin

• There was no significant difference in cycle length between non-treated and estrogen-treated mares. However, altrenogest-treated mares showed notably longer cycle lengths.
• Estradiol benzoate influenced the uterine PI values only on the day of administration (Day 0) where uterine PI values decreased from Day 0 to Day 1 in estrogen-treated mares but increased in untreated cycles.
• Mean PI values for both the uterine and ovarian arteries, during both estrus and diestrus, were higher in estrogen-treated mares when compared to non-treated mares.
• Similarly, altrenogest-treated mares had greater mean uterine PI values during both phases of the cycle.
• No significant immediate effect on ovarian PI values was detected in response to either estrogen or altrenogest treatments.
• Elevated mean ovarian PI values were only observed in estrus following altrenogest administration, compared to untreated cycles.

Conclusion

• Gathering the study’s data on the impact of exogenous hormones on genital perfusion in cycling mares, the researchers concluded that both exogenous estrogen and progestin decreased genital perfusion in cycling mares.
• This finding potentially impacts our understanding of fertility in mares, suggesting an avenue for further studies to explore how modulating hormone levels might affect mare fertility and cycle lengths.