Season of the year influences concentration and pattern of gonadotropins and testosterone in circulation of the bovine male.

Serum concentrations of LH vary with season of the year in ovariectomized beef and dairy cows. The objective of the present study was to determine whether concentrations and profile of the gonadotropins and testosterone (T) in circulation vary with season of year in bovine males of a composite breed type (beef). Five INTACT and five gonadectomized (GNX) males that were 22 mo of age at the initiation of the study were used. All of the males utilized were maintained on pasture throughout the year at the latitude of 41 degrees N. Blood samples were collected in a serial regimen (10-min intervals for 24 h) at the spring and fall equinox and the summer and winter solstice. Concentrations of LH were quantified in all samples, and concentrations of T were determined in all samples of the INTACT group. Concentrations of FSH and 17 beta-estradiol (E2) were quantified in pooled samples for all animals, while concentrations of T were determined in pooled samples for males from the GNX group. Pulse frequency of LH or T and mean concentration of FSH did not vary with season of the year. A seasonal effect on mean concentration of LH (p < 0.01) occurred in males of the GNX group, with mean concentrations of LH being greatest during the spring equinox and lowest during the winter solstice. Season had an effect on pulse amplitude of LH (p < 0.01), mean concentration of T (p < 0.01), and pulse amplitude of T (p < 0.05) in males from the INTACT group.(ABSTRACT TRUNCATED AT 250 WORDS)