GROWTH AND REPRODUCTIVE DEVELOPMENT IN BRAHMAN BULLS FED DIETS CONTAINING GOSSYPOL

To determine the effect of gossypol on growth and reproductive development, Brahman bulls (n = 30) were fed diets containing gossypol(6 or 60 mg kg BW-1 d(-1) or a diet free of gossypol from weaning through puberty. Diets contained cottonseed meal (CSM), whole cottonseed (WCS), or soybean meal (SBM) as the major sources of dietary CP. Diets were formulated to provide similar NE(g) for medium-framed bulls to gain .9 kg/d. Measurements of BW and scrotal circumference were obtained at 28-d intervals, and beginning at 10 mo of age electroejaculates were collected at 14-d intervals. By 196 d on feed, bulls fed WCS had gained less (P <.05) BW and tended (P < .10) to have lower gain/feed than bulls fed CSM. When spermatozoa were first detected in an ejaculate, bulls fed CSM tended (P <.10) to be younger than bulls fed WCS (357 vs 386 d; SBM = 380 d); bulls fed SBM were heavier(P <.05) than bulls fed gossypol (333 vs 310 kg), but they had similar scrotal circumferences. Bulls fed WCS reached puberty at an older (P <.05) age (613 d) than bulls fed CSM (528 d; SBM = 550 d) but had similar BW and scrotal circumferences. Electroejaculated semen quality and quantity did not differ (P >.10) between treatments at puberty. Seminiferous tubule diameters did not differ(P >.10) among treatments, but bulls fed diets that contained gossypol had larger (P <.01) lumenal diameters, smaller (P <.01) germinal epithelium thicknesses, and fewer (P <.01) germ cell layers than bulls fed SBM diets. Circulating concentrations of testosterone at three stages of maturity were not affected(P >.10) by diet. In summary, bulls fed WCS reached puberty at an older age but had similar BW as bulls fed SBM or CSM. Gossypol affected testicular morphology but did not affect semen quality at puberty; the mechanism cannot be determined from this study.