Effects of GnRH treatment on scrotal surface temperatures in bulls

Two experiments were conducted to characterize scrotal surface temperature (SST) in bulls treated with gonadotropin releasing hormone (GnRH). In Exper iment 1, Angus bulls (n = 10, 18 mo, 597 kg) were given GnRH (400 ng/kg) or saline, IV. Bottom SST increased approximately 1.7 degreesC (P < 0.005) ov er time (0 to 90 min) at an ambient temperature of 5<degrees>C. However, th ere was no significant effect of GnRH treatment and temperature increases w ere attributed to stress. When the experiment was repeated at an ambient te mperature of 25 degreesC, SST was elevated prior to treatment, with no subs equent significant increase. Experiment 2 was conducted with Charolais bull s (n = 6, 12-14 mo, 517 kg) with an emphasis on minimizing stress. Bottom S ST increased approximately 2 degreesC (P < 0.05) between 0 and 45 min after GnRH treatment, supporting the hypothesis that GnRH treatment increases SS T in bulls. In conclusion, it was apparent that stress, high ambient temper atures, and GnRH treatment can all increase SST in bulls.