Relationships between blood and follicular fluid urea nitrogen concentrations and between blood urea nitrogen and embryo survival in mares.

This research looked into how high blood urea nitrogen (BUN) potentially affects fertility in mares specifically, which had not been previously proven. Two experiments were conducted, one looking at the relationship between BUN and follicular fluid urea nitrogen (FUN), and another at how BUN in embryo donor mares influences pregnancy outcomes. The results suggest a strong correlation between BUN and FUN, and a higher level of BUN in mares with unsuccessful embryos. The donor mares’ age and lactation also seemed to impact the embryos’ survival after being transferred to recipient mares.

Understanding the Research

• The study primarily sought to explore the relationship between blood urea nitrogen (BUN) and follicular fluid urea nitrogen (FUN) and its impact on fertility in mares. Previous studies had indicated a correlation between high BUN and low fertility in cows and ewes, but this connection was not previously proven in mares.
• To explore this relationship, the researchers conducted two experiments. One focusing on the linkage between BUN and FUN during follicle growth, and another seeing how BUN from embryo donors affected pregnancy outcomes in recipient mares.

Follicular Fluid and Blood Samples Collection

• To explore the relationship between BUN and FUN, the researchers collected follicular fluid and blood samples from mares during two stages: diestrus (when the mares had growing follicles) and estrus (when they had pre-ovulatory follicles).
• In comparing the collected samples, the researchers found a strong positive correlation between BUN and FUN. This indicates that the nitrogen content in the mare’s blood is connected to the nitrogen content in their follicular fluid. This was particularly true with mares that had growing follicles somewhat more than those with pre-ovulatory follicles.

Impact on Embryo Survival and Fertility

• Further, the researchers studied how BUN relates to pregnancy outcomes. This was done by looking at BUN levels and seeing whether donor mares who had unsuccessful embryos had higher BUN than those who had successful pregnancies.
• The study found out that BUN was indeed higher in donor mares that had unsuccessful embryos. This suggests that high BUN could be responsible for lower fertility in mares, similar to the situation in cows and ewes.
• However, it wasn’t just BUN at play. The research also showed that older donor mares and those with certain lactation patterns had less successful embryo survival after transfer. That is, age and lactation also affect the survivability of the embryos transferred to recipient mares, not just the BUN levels.

Conclusion

• Overall, the experiments provided evidence that BUN is associated with the follicular fluid environment and the survival rate of embryos after transfer to recipient mares. This implies that BUN, in addition to age and lactation of the donor mares, has an impact on mare fertility.