GROWTH AND REPRODUCTIVE DEVELOPMENT IN BRAHMAN BULLS FED DIETS CONTAINING GOSSYPOL

To determine the effect of gossypol on growth and reproductive develop ment, Brahman bulls (n = 30) were fed diets containing gossypol(6 or 6 0 mg kg BW-1 d(-1) or a diet free of gossypol from weaning through pub erty. Diets contained cottonseed meal (CSM), whole cottonseed (WCS), o r soybean meal (SBM) as the major sources of dietary CP. Diets were fo rmulated to provide similar NE(g) for medium-framed bulls to gain .9 k g/d. Measurements of BW and scrotal circumference were obtained at 28- d intervals, and beginning at 10 mo of age electroejaculates were coll ected at 14-d intervals. By 196 d on feed, bulls fed WCS had gained le ss (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 goss ypol (333 vs 310 kg), but they had similar scrotal circumferences. Bul ls 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 circumfer ences. 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 contain ed gossypol had larger (P <.01) lumenal diameters, smaller (P <.01) ge rminal epithelium thicknesses, and fewer (P <.01) germ cell layers tha n bulls fed SBM diets. Circulating concentrations of testosterone at t hree 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 b ulls fed SBM or CSM. Gossypol affected testicular morphology but did n ot affect semen quality at puberty; the mechanism cannot be determined from this study.