Effects on Testosterone, LH and Cortisol Concentrations, and on Testicular Ultrasonographic Appearance of Induced Testicular Degeneration in Bulls

It is well known that heat stress has a detrimental effect on testicular functions. In addition to the alteration of semen quality and testicular damage, reproductive hormone secretion can be altered. The objective of this study was to decribe changes in plasma concentrations of testosterone, LH and Cortisol, as well as in testicular ultrasonographic appearance after induced testicular degeneration. Four Swedish Red and White bulls, aged 3 years, were used. They were fed according to Swedish standards. The scrotum was covered with an insulation device during 96 h. Semen was collected weekly 3 times before and up to 4 months after insulation. Testicular ultrasonography and clinical genital examination were performed with the same intervals. Heparinized blood samples were taken from the jugular vein at 2 h interval during 24 h every 2 weeks during the study. Blood samples were tested for the content of testosterone, LH and Cortisol. Data were analysed, using oneway analysis of variance of seminal data, clinical examination data as well as 24 h hormonal output data as perentage of mean individual pretreatment values. The use of a 5 MHz B-mode ultrasound unit did not contribute with an objective estimation of the degree of testicular degeneration. In 3 of the bulls testosterone levels had a tendency to decrease and LH to increase during the time of severe degeneration, whereas an opposite trend was seen during the regenerative phase, changes becoming significant 15 weeks after scrotal insulation. Variation between animals was big. Cortisol levels had a decreasing trend, changes being significant only in individual bulls at 10 and 15 weeks after scrotal insulation. One bull had to be treated separately as testosterone and LH patterns were deviating. It was concluded that severe testicular degeneration induces related changes in the levels of testosterone and LH.