Horse Clinical Cytogenetics: Recurrent Themes and Novel Findings.
Authors: Bugno-Poniewierska Monika, Raudsepp Terje
Journal: Animals : an open access journal from MDPI
Summary
Chromosomal abnormalities represent a significant but often overlooked cause of reproductive failure and congenital defects in horses, occurring in approximately 30% of animals presenting with fertility or developmental problems compared to just 2–5% of clinically normal populations. Over five decades of clinical cytogenetic research has identified two recurrent and species-characteristic conditions—X-monosomy (35% of all equine chromosome aberrations) and SRY-negative XY sex reversal (11%)—which are rarely encountered in other domestic species and warrant particular attention in breeding programmes. Modern molecular genomic tools have substantially refined our ability to characterise chromosomal aberrations and elucidate their underlying mechanisms, moving beyond traditional karyotyping. Despite these technological advances, conventional cytogenetics remains the most practical, economical, and rapid initial screening method for evaluating breeding soundness and investigating reproductive or developmental disorders in the clinic. For farriers, veterinarians, and allied professionals involved in performance and breeding management, awareness of these recurrent conditions and readiness to recommend chromosomal analysis when appropriate—particularly for young stock with developmental anomalies or breeding animals with unexplained infertility—represents a straightforward opportunity to improve outcomes and make more informed management decisions.
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Practical Takeaways
- •When evaluating horses with fertility problems or developmental issues, request cytogenetic analysis as chromosomal abnormalities are found in nearly 1 in 3 affected animals
- •Be aware that X-monosomy and sex reversal conditions are particularly common in horses and should be suspected in mares with reproductive failure or stallions with low fertility
- •Standard karyotyping remains the practical first-line diagnostic tool for breeding soundness evaluation and investigation of developmental problems
Key Findings
- •Approximately 30% of horses with reproductive or developmental problems have chromosome aberrations compared to only 2-5% in the general population
- •X-monosomy and SRY-negative XY sex reversal account for approximately 35% and 11% of all equine chromosome abnormalities respectively, making them signature conditions for the species
- •Traditional cytogenetics remains the most straightforward, cost-effective, and fastest approach for initial evaluation of breeding animals despite advances in molecular genomics tools