Effect of season and location on semen quality and serum concentrations of luteinizing hormone and testosterone in Brahman and Hereford bulls.
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abstract
Hereford bulls from Montana (MH; n = 15) and Nebraska (NH; n = 15) and Brahman bulls from Texas (BB; n = 18) were relocated to one of three locations (LOC): Montana (MT), Nebraska (NE) or Texas (TX). All bulls were pubertal at the time of relocation in late May 1984. Semen was collected by electroejaculation within 1 wk after relocation and at 90-d intervals beginning in November 1984 through early February 1986. Bulls were given a GnRH challenge (200 micrograms i.m.) during the same week of semen collections. Bulls also were bled for 8 h at 20-min intervals in the fall of 1984 and the spring and fall of 1985 to determine endogenous concentrations of LH and testosterone. Season affected sperm concentration in all breeds (P less than .05) with decreases during the winter in BB and during the summer in NH and MH bulls. Brahman bulls had lower percentage of live cells (LIVE) than NH and MH bulls did (P less than .0001). Brahman bulls decreased in LIVE during the winter (P less than .001). Area under the LH curve after GnRH was lower (P less than .005) in BB than in MH and NH. Brahman bulls in MT had greater (P less than .02) area under the LH curve and lower (P less than .06) area under the testosterone curve than did BB in TX or NE during the winter. There was no seasonal fluctuation in LH or testosterone response to GnRH in NH or MH bulls at any LOC. Area under the endogenous LH curve was lowest (P less than .04) in BB. Basal endogenous testosterone concentration was greater (P less than .03) in NH than in MH or BB. Area under the endogenous testosterone curve was lower (P less than .03) in MH than in NH or BB. These results indicate that BB exhibit seasonal fluctuations in semen quality. This was not so apparent in semen quality traits of Hereford bulls. There also was a seasonal influence in BB on both endogenous testosterone and GnRH-stimulated LH and testosterone concentrations. Compared with Hereford bulls, Brahman bulls had lower endogenous and GnRH-stimulated concentrations of LH.
