ESTIMATES OF GENETIC-PARAMETERS FOR 320-DAY PELVIC MEASUREMENTS OF MALES AND FEMALES AND CALVING EASE OF 2-YEAR-OLD FEMALES

Records from 12 breed groups collected from 1983 to 1991, included in the Germ Plasm Utilization project at the U.S. Meat Animal Research Ce nter, were analyzed separately by breed group and combined to estimate heritabilities and genetic correlations for 320-d male and female pel vic width, height, and area, and for 320-d male pelvic and female 2-yr -old calving ease. Calving ease was analyzed as a trait of the dam usi ng 1) actual and 2) binary scale calving ease scores with-a covariate of calf birth weight. A bivariate animal model and derivative-free REM L incorporating sparse matrix techniques were used. When breed groups were analyzed separately, heritability estimates of male and female 32 0-d pelvic traits varied by breed group and sex. Average genetic corre lations between male and female 320-d pelvic width, pelvic height, and pelvic area were large and positive. When breed groups were combined (n 26,071), heritability estimates for 320-d pelvic traits were modera te in size. Genetic correlations of .68, .48, and .61, between male an d female 320-d pelvic width, height, and area, respectively, suggest m ale and female pelvic traits are largely under the same genetic contro l but are correlated traits rather than the same trait. Heritability e stimates for actual calving ease in 2-yr-olds ranged from .00 to .49 i n separate breed group analyses, and from .00 to .37 for binary measur es. When breed groups were combined, heritability was .11 for actual c alving ease and was .09 on the binary scale. Genetic correlations by b reed groups between 320-d male pelvic traits and calving ease of 2-yr- old females were variable. When breed groups were combined, genetic co rrelation estimates between 320-d male pelvic traits and actual calvin g ease of 2-yr-old females (on a B-point scale) were negative and mode rate as were genetic correlations between male 320-d pelvic traits and binary calving ease of 2-yr-old females. A bull one phenotypic SD abo ve the mean in pelvic area would be expected to increase his daughters ' average pelvic area by 1.30 cm(2) and improve its calving ease score by .03 of a score compared with an average breed bull.