ESTIMATION OF GENETIC-PARAMETERS FOR SCROTAL CIRCUMFERENCE, AGE AT PUBERTY IN HEIFERS, AND HIP HEIGHT IN BRAHMAN CATTLE

Genetic parameters were estimated for scrotal circumference (SC; n = 2 87), age at puberty in heifers (AP; n = 292), and hip height in both s exes (HH; n = 684) for Brahman cattle born from 1984 to 1994 at the Su btropical Agricultural Research Station, Brooksville, Florida. Age at puberty was defined as the age (days) at first detected ovulatory estr us. Measurements of SC and HH were taken at 18 mo of age. Fixed effect s considered in the SC model were year of birth (YOB), age of dam (AOD ), and age at measurement (AGE) as a linear covariate. Fixed effects f itted to the AP model were YOB and AOD. Fixed effects in the HH model were YOB, sex, AOD, and AGE as a linear covariate. Variances and covar iances were estimated using REML with a derivative-free algorithm and fitting a multiple trait animal model. Estimates of heritability for S C, AP, and HH were .28, .42, and .65, respectively. Estimates of genet ic correlations between SC and AP, SC and HH, and AP and HH were -.32, .19, and .25, respectively. Estimates of environmental correlations w ere .19 between SC and HH, and -.13 between AP and HH. Estimates of ge netic parameters indicate a favorable genetic relationship between SC in Brahman bulls and AP in Brahman heifers under subtropical condition s. There was also evidence that selecting Brahman bulls for HH would n ot adversely affect SC but would have some detrimental effect on AP in female progeny.