Testosterone effects on gonadotropin response to GNRH: cows and pony mares.

This research investigates the impact of testosterone treatment on hormone concentrations in cows and pony mares. Demonstrating varied findings between species, results suggest testosterone may play a role in hormonal regulation in ponies, but less so in cows.

Objective and Methodology

• The study aimed to know how testosterone propionate (TP) affects the levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the plasma of ovariectomized (surgically altered to stop ovulation) cows and pony mares.
• The researchers performed an initial injection of gonadotropin-releasing hormone (GnRH) followed by testosterone treatment or control injections for a duration of 10 days for cows and 11 days for ponies.
• A second GnRH injection was given a day after the final TP or oil injection, and LH and FSH concentrations were measured before and after each GnRH injection.

Findings and Implications

• The control injections did not change the response to GnRH or the pre-GnRH concentrations of LH and FSH in ovariectomized cows or ponies.
• In the pony mares, testosterone treatment increased the release of FSH in response to GnRH nearly five times—an effect not observed in the cows even though the average daily testosterone level was 59% higher than in the ponies.
• Contrarily, testosterone treatment reduced the release of LH in response to GnRH by 26% in ovariectomized pony mares and 17% in ovariectomized cows.
• The outcomes suggest that ovarian androgens, such as testosterone, may — but not definitely — have a role in FSH secretion regulation during the estrous cycle of the mare. This implication, however, was not supported for cows in this study.

Conclusion

• The study illustrates the distinct effects of testosterone on hormonal responses in different species. The testosterone had a significant influence on FSH and LH secretion in ovariectomized pony mares, but not on cows, even with a higher average daily concentration of testosterone.
• This research could be fundamental in understanding how testosterone affects hormonal regulation in different species. They offer a unique perspective for fertility treatments and management, especially for mares.