An update of chromosomal abnormalities in mares

Area of Science:

• Veterinary Genetics
• Equine Reproduction
• Cytogenetics

Background:

• Gonadal dysgenesis (GD) in mares is often associated with chromosomal abnormalities.
• Understanding these abnormalities is crucial for diagnosing and managing reproductive issues in horses.

Purpose of the Study:

• To investigate the prevalence and types of chromosomal abnormalities in mares with gonadal dysgenesis.
• To report novel chromosomal abnormalities and a rare case of fertility in affected mares.

Main Methods:

• Karyotyping of mares diagnosed with gonadal dysgenesis using G-banding and C-banding techniques.
• Analysis of chromosomal complements in yearling fillies presenting with poor development and lack of vigor.
• Blood typing to confirm parentage in a unique case of a foal born to a mare with gonadal dysgenesis.

Main Results:

• Chromosomal abnormalities were detected in 98 out of 180 mares (aged 3 years and older) with gonadal dysgenesis.
• The most frequent abnormality was X monosomy (63,X), followed by a male-like karyotype (64,XY).
• Two mares had a previously unreported structural X chromosome abnormality [64,X,del(Xp)], with one successfully foaling a filly with the same karyotype, confirming fertility.

Conclusions:

• Chromosomal abnormalities are a significant factor in equine gonadal dysgenesis.
• Novel karyotypes, including structural X chromosome abnormalities and autosomal trisomy, have been identified in horses.
• Fertility in mares with gonadal dysgenesis and chromosomal abnormalities, though rare, is possible and has been documented.