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 ovariectomi zed beef and dairy cows. The objective of the present study was to det ermine whether concentrations and profile of the gonadotropins and tes tosterone (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 collecte d in a serial regimen (10-min intervals for 24 h) at the spring and fa ll equinox and the summer and winter solstice. Concentrations of LH we re quantified in all samples, and concentrations of T were determined in all samples of the INTACT group. Concentrations of FSH and 17beta-e stradiol (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 FS H did not vary with season of the year. A seasonal effect on mean conc entration of LH (p < 0.01) occurred in males of the GNX group, with me an concentrations of LH being greatest during the spring equinox and l owest during the winter solstice. Season had an effect on pulse amplit ude of LH (p < 0.01), mean concentration of T (p < 0.01), and pulse am plitude of T (p < 0.05) in males from the INTACT group. Pulse amplitud e of LH was greatest at the spring equinox in INTACT males, while the greatest mean concentration and pulse amplitude of T occurred at the s ummer solstice in INTACT males. Scrotal circumference tended to vary ( p = 0.06) with season in INTACT males and followed the same pattern as T. In summary, the profile of LH and T in circulation varies with sea son of the year in the bovine male.