Abstract
Thyroid hormones regulate a wide range of physiological functions and are synthesized in response to thyroid-stimulating hormone (TSH). The present study aimed to examine the regulatory influence of heterologous TSH on thyroid activity in three duck species. In vitro formation of thyroxine (T(4)) and triiodothyronine (T(3)) in the thyroids of adult Muscovy ducks (Carirana moschata), common ducks (Anas platyrhynchos domesticus), and mule ducks (hybrids of male C. moschata and female A. platyrhynchos domesticus) were examined following stimulation with ovine TSH (oTSH) across different times (0.5 to 12 h) and dosages (1 to 100 ng). The concentration of T(4) and T(3) increased in a time- and dose-dependent manner, indicating that duck thyroids were responsive to oTSH and capable of de novo hormone synthesis. Despite their significantly lower body weights, male and female common ducks exhibited significantly higher thyroid hormone concentrations and T(3)/T(4) ratios than the other species (P < 0.05). Male Muscovy ducks secreted significantly more T(4) (P < 0.05), whereas female ducks displayed higher T(3) levels and T(3)/T(4) ratios (P < 0.05). No significant differences were observed in thyroid hormone concentrations or T(3)/T(4) ratios between Muscovy and mule drakes (P > 0.05). These findings provide the first evidence that oTSH can stimulate thyroid activity in ducks, supporting the conserved nature of TSH-receptor interactions across vertebrates and offering a practical basis for developing thyroid bioassays for poultry research.