GROWTH AND REPRODUCTIVE DEVELOPMENT FROM WEANING THROUGH 20 MONTHS OFAGE AMONG BREEDS OF BULLS IN SUBTROPICAL FLORIDA

To determine the effect of breed on growth and reproductive developmen t. weaned bulls in each of 2 yr were managed as a single group for app roximately a year. In Year 1, the study group consisted of 24 Angus, 2 4 Brahman. 20 Hereford and 14 Senepol bulls, while in Year 2. it conta ined 25 Angus, 17 Brahman. 13 Romosinuano and 9 Nellore x Brahman bull s. Body and testicular growth measurements were recorded at 6-wk inter vals. At approximately 1 yr of age and quarterly thereafter (4 periods ). bulls were evaluated for libido. pubertal status, and GnRH-induced LH and testosterone secretion. Significant breed-by-age interactions o ccurred for most growth measurements. Brahman bulls (Bos indicus) were (P<0.05) older and heavier at puberty than Angus, Hereford. Senepol a nd Romosinuano bulls (Bos taurus). Libido scores were lowest for Brahm an and Nellore X Brahman bulls (Bos indicus), highest for Angus and He reford bulls (temperate Bos taurus breeds) and intermediate for Senepo l and Romosinuano bulls (tropical Bos taurus breeds; P<0.05). Differen ces were not consistent among breeds or between years for GnRH-induced LH secretion. In both years, basal testosterone concentrations and ar eas under the GnRH-induced testosterone curve were higher (P<0.05) for Angus and Hereford bulls (temperate breeds) than for Brahman. Senepol , Romosinuano and Nellore X Brahman bulls (tropical breeds). In conclu sion, reproductive development of Senepol and Romosinuano bulls (tropi cal Bos taurus breeds) was more similar to Angus and Hereford bulls (t emperate Bos taurus breeds) than to Brahman and Nellore X Brahman bull s (Bos indicus). (C) 1997 by Elsevier Science Inc.