Androgens and oestrogens in normal and cryptorchid stallions.

The study investigates the levels of total androgens, testosterone, and total oestrogens in different categories of stallions, including intact, unilaterally cryptorchid, bilaterally cryptorchid stallions, and geldings. The research uncovers significant differences in hormone levels among the groups, with notable effects of castration, sexual stimulation, and season on androgenic function.

Hormone Levels in Different Categories of Stallions

• Twenty-one intact, nine unilaterally cryptorchid, three bilaterally cryptorchid stallions, and four geldings were studied for their hormone levels.
• Total oestrogens were found to be significantly higher in bilaterally cryptorchid stallions compared to other groups (P < 0.005).
• Total androgens were significantly lower in the bilateral cryptorchid group (P < 0.05).

Day and Night Variation in Androgen Levels

• The study observed a significant day and night variation in total androgen levels (P < 0.025), revealing a fluctuation in hormone levels throughout a 24-hour period.

Seasonal Effect on Androgenic Function

• Both thyroidectomized and intact animals showed a marked decrease in total androgen and testosterone levels during the winter period, indicating a seasonal effect on the androgenic function of the testis.

Effects of Castration and Sexual Stimulation

• The disappearance rate of total androgens following castration was extremely rapid, with levels becoming undetectable within 12 hours.
• Sexual stimulation appeared to increase total androgen levels, suggesting a link between sexual activity and hormone production.

Identification of Androgens

• Various androgens, including testosterone, androstenedione, dihydrotestosterone, androstandiols, and androstenediol, were identified in spermatic vein blood.
• Dihydrotestosterone was also measured in fluid from the cauda epididymidis.

Conclusion and Implications

• The study provides insights into the hormonal profile of different categories of stallions, shedding light on factors such as cryptorchidism, castration, sexual stimulation, and seasonal changes that affect hormone levels.
• Understanding these dynamics can contribute to better management practices in equine reproduction, health, and behavior.
• The rapid disappearance of androgens following castration and the identification of specific androgens in various reproductive tissues add valuable information to the field of equine endocrinology.