Serum and seminal thyroid hormones in relation to semen quality of Friesian bulls

Serum and seminal levels of thyroxine [T[4]] and triiodothyronine [T[3]] were evaluated and correlated with the semen quality of two groups of Friesian bulls. The first group [I] was of high semen quality while the second [II] represented bulls of moderate quality. Obtained data clarified that serum T[4] and T[3] levels were significantly higher in bulls of group I than those of group II. Serum T[4]/T[3] ratio was nearly similar in both groups. Seminal plasma T[3] contents of group I were higher than their corresponding values of group II, while T[4] concentrations of the second group were sharply greater than those of the first group. It was concluded that a reverse relationship is found between seminal T[4]/T[3] ratio and semen quality. T[3] has the upper hand in regulating semen activity. Decreased conversion of T[4] into T[3] in semen leads to an imbalance among both hormones which could be considered as a factor responsible for inhibited sperm activity