Elevated plasma testosterone concentrations during stallion-like sexual behavior in mares (Equus caballus)

Area of Science:

• Equine behavior
• Reproductive endocrinology
• Animal behavior

Background:

• Mounting behavior in mares is not fully understood, especially in the absence of stallions.
• Previous research has not extensively linked this behavior to hormonal profiles and the estrous cycle stage.

Purpose of the Study:

• To investigate mounting interactions in mares isolated from stallions.
• To determine the relationship between mounting behavior, the estrous cycle stage, and circulating hormone levels.

Main Methods:

• Observations of mounting behavior in a herd of 105 mares over 3 years.
• Hormonal analysis (testosterone, androstenedione, estradiol, estrone, progesterone) and transrectal ultrasonography were performed post-interaction.

Main Results:

• Mounting interactions were rare (15 observed over 3 years) and predominantly occurred during the follicular phase.
• Mares exhibiting mounting behavior had significantly higher testosterone concentrations compared to mares in the standing and control groups.
• No significant differences were found in follicle size, number, or other hormone levels among the groups.

Conclusions:

• Mare-to-mare mounting is infrequent and primarily associated with the follicular phase of the estrous cycle.
• Elevated testosterone levels appear to be a key factor influencing mounting behavior in mares.
• This behavior may serve a social or reproductive function independent of stallion presence.