Concentration of serum testosterone in XY sex reversed horses.

This research investigated the levels of serum testosterone in horses with XY sex reversal syndrome, a condition where genetically male horses show female or intersexual traits. The study found that hormone levels varied according to the degree of sex reversal and may be used as an additional factor in understanding this condition.

Background of XY Sex Reversal Syndrome in Horses

• XY Sex Reversal Syndrome is a condition observed in horses, where genetically male horses (XY) exhibit female or intersexual physical and behavioral characteristics.
• The researchers had previously classified 38 sex-reversed XY mares into four classes (Class I to IV), based on their behavior, physical phenotype, gonadal status, and H-Y phenotype. In simple terms, Class I horses were near-normal females possibly capable of fertility, while Class IV represented strongly virilized intersex horses.

Objective of the Current Research

• The present study aimed to measure serum testosterone concentrations in these sex-reversed XY mares, along with a few control samples taken from normal mares and stallions.
• The objective was to explore if hormonal levels could exhibit a correlation with the severity of sex reversal and can be utilized as a diagnostic or research tool in understanding XY sex reversal syndrome.

Study Sample and Methodology

• The test samples were taken from 29 sex-reversed XY mares, along with 3 normal mares (XX), and 3 normal stallions (XY) as controls.
• The samples were collected during the breeding season (March-August) and preserved at -70 degrees Celsius until further analyses were conducted.

Findings of the Study

• Serum testosterone concentrations in normal mares ranged from nondetectable to 0.41 ng/ml, in normal stallions they ranged from 1.04 ng/ml to 2.4 ng/ml, while in sex reversed XY mares, they ranged from nondetectable to an exceptionally high 5.4 ng/ml.
• Testosterone concentrations in sex reversed classes I and II (more ‘female’ types) ranged from nondetectable to 0.22 ng/ml.
• There was a clear correlation between serum testosterone levels in XY mares and their sex phenotype and behavior. Higher testosterone levels were observed in horses with stronger male traits.

Conclusions and Significance

• The study concluded that testosterone concentrations may well serve as a useful additional parameter in the study of the XY sex reversal syndrome in horses.
• While increasing the sample size might provide more accurate quantification of the hormone ranges among XY mares, the collected data still indicated that testosterone levels could be linked with the degree of sex reversal in affected horses.