Genetic and environmental parameters for traits derived from the Brody growth curve and their relationships with weaning weight in Angus cattle

Direct and maternal genetic and environmental variances and covariances wer e estimated for weaning weight and growth and maturing traits derived from the Brody growth curve. Data consisted of field records of weight measureme nts of 3,044 Angus cows and 29,943 weaning weight records of both sexes. Gr owth traits included weights and growth rates at 365 and 550 d, respectivel y. Maturing traits included the age of animals when they reached 65% of mat ure weight, relative growth rates, and degrees of maturity at 365 and 550 d . Variance and covariance components were estimated by REML from a set of t wo-trait animal models including weaning weight paired with a growth or mat uring trait. Weaning and cow contemporary groups were defined as fixed effe cts. Random effects for weaning weight included direct genetic, maternal ge netic, and permanent environmental effects. For growth and maturing traits, a random direct genetic effect was included in the model. Direct heritabil ity estimates for growth traits ranged from .46 to .52 and for maturing tra its from .31 to .34. Direct genetic correlations between weaning weight and weights and growth rates at 365 and 550 d ranged from .56 to .70. Correlat ions of maternal weaning genetic effects with direct genetic effects on wei ghts at 365 and 550 d were positive, but those with growth rates were negat ive. Between weaning weight and degrees of maturity at both 365 and 550 d, direct genetic correlation estimates were .55 and maternal genetic correlat ions estimates were -.05, respectively. Direct genetic correlations of wean ing weight with relative growth rates and age at 65% of mature weight range d from .04 to .06, and maternal-direct genetic correlation estimates ranged from -.50 to -.56, respectively. These estimates indicate that higher gene tic capacity for milk production was related to higher body mass and degree s of maturity between 365 and 550 d of age but was negatively related to ab solute and relative growth rates in that life stage.