Behavioral characteristics of beef steers administered estradiol, testosterone and dihydrotestosterone

Twelve beef steers ranging in age from 6 to 8 mo were randomly assigned to one of four steroid treatment groups so the ability of each hormone to stimulate sexual and(or) agonistic behavior could be assessed. The steers received im injections of either 200 mg of testosterone (T), 200 micrograms of estradiol-17 beta (E2), 200 mg of dihydrotestosterone (DHT) or sesame oil vehicle as control (C), every other day for 10 d. During these 10 d, behavior was studied for 60 min at 0600, 1200, 1800 and 2400 h. Peak activity occurred during the first half of the experiment with maximum behavioral expression observed at the 2400-h observation period. Estradiol was most effective in stimulating eight of the 13 behaviors studied. These included: sniffs received, sniffs given, successful mounts, chin rests given, chin rests received, stands to be mounted, refusals to stand and head butts received. Testosterone was most effective in stimulating Flehmen lip curls, attempted mounts and head butts given. Testosterone significantly increased activity in seven other categories over that of controls. Dihydrotestosterone was never the most effective steroid. It was capable of stimulating several of the behaviors studied above that of controls, but reduced mounting activity of steers. In view of the major responses observed with E2 and the aromatizable androgen, T, these data are interpreted as an indication that E2 plays a significant direct role in sexual behavior in the male bovine.