X chromosome aneuploidy and micronuclei in fertile mares.

The research examines the relationship between chromosomal abnormalities, specifically in the form of 63,X mosaicism, and fertility in mares. Despite finding 27% of fertile mares were 63,X mosaics, the rates of abnormal cells were low, indicating minor influence on fertility. However, mares with a higher incidence of such cells could have a higher fertility risk.

Objective of the Research

• The research aimed to gain a better understanding of the influence of X chromosome aneuploidy, specifically a condition called 63,X mosaicism, on the fertility of mares. This abnormality is often challenging to detect during routine evaluations as its clinical significance is yet to be fully understood.

Study Design

• The study involved investigating the prevalence and levels of 63,X mosaicism in a group of fertile mares, and comparing these with eight ‘problem’ mares that were experiencing sub-fertility issues for unknown reasons.
• The researchers also analysed micronuclei, which are indicators of genomic instability and can affect cell division, thus leading to cancer or congenital diseases.

Findings

• The study found that although 27% of the fertile mares were identified as 63, X mosaics, the rates of abnormal cells were quite low (only 1-3%).
• The rate of micronuclei in the blood of these mares was around 1%, which is significantly lower than the 5% baseline proposed for healthy humans.
• The fertile mares with 63,X mosaicism had similar or higher levels of abnormal cells as the problem mares.

Statistical Correlation

• Correlations between the age of the fertile mares and 63,X cells, and between the rate of micronuclei, were weak to modest and not statistically significant (p > 0.05).
• Similarly, there was no significant correlation between the presence of a 63,X cell line and the micronuclei rate.

Conclusion and Recommendations

• The presence of 63,X cells in rates exceeding 3% may actually indicate a higher risk for sub-fertility and potentially related health problems in such mares.
• Detecting and eliminating mares with high levels of X aneuploidies from breeding could have a beneficial effect on the overall fertility within the general horse population.
• This research could aid the assessment of mares with mosaic karyotypes involving the X chromosome, those mares that are exhibiting fertility issues without clear clinical reasons.