Development of sexual and aggressive behaviors in Hereford bulls.

The purpose of this study was to describe maturation-related changes in the sexual and aggressive behaviors of Hereford bulls. Two groups of 13 and 14 bulls, respectively, were tested for sexual and aggressive behaviors every 3 mo from 3 to 24 mo of age. At 3 and 6 mo of age, the bulls were exposed, as groups, to two estrous females, whereas at 9, 12, 15, 18, 21, and 24 mo these bulls were tested under each of the following several treatment conditions: 1) individual tests (single males were exposed to single females), 2) small-group tests (three or four bulls:three females), 3) large-group tests (13 or 14 bulls:3 females), and 4) male-only tests (13 or 14 bulls were placed in the test arena in the absence of females). Most bulls consistently mounted females by 9 mo of age. Twenty-one of the 27 bulls (78%) attained their first ejaculation at either 12 or 15 mo of age. The frequency of mounting without ejaculation was greatest in large-group tests at 12 mo of age, and ejaculation frequency peaked at 18 mo. The incidence of male-male mounting in large-group tests (with females) did not appreciably change from 3 to 24 mo, whereas male-male mounting in male-only tests was greatest at 9 and 24 mo. We conclude that sexual performance data obtained in serving capacity tests administered to yearling bulls before 18 mo of age may underestimate the mating potential of certain individuals.(ABSTRACT TRUNCATED AT 250 WORDS)