Running Head : Correlations between reproduction and growth Estimates Of Covariances Between Reproduction And Growth In Australian Beef Cattle1

Estimates of covariance components between scrotal circumference, serving capacity, days to calving, yearling and final weight were obtained for Hereford, Angus and Zebu cross cattle in temperate and tropical Australia. Analyses were carried out by restricted maximum likelihood employing a derivative-free algorithm and fitting bivariate animal models. Aspects of modeling and computational requirements related to the use of this method are discussed. Estimates of heritabilities agreed closely with those from univariate analyses, being low for female reproductive performance and moderate to high for male reproduction and growth. Estimates of genetic correlation between male and female fertility traits were low but favorable, being -.25, -.28 and -.41 between scrotal circumference and days to calving for Herefords, Angus and Zebu crosses, respectively. Genetic correlations between male reproductive traits and weights ranged from .24 to .52 for the temperate breeds and were higher (.65 to .69) for Zebu Crosses. Phenotypic correlations between scrotal circumference and weights were similar for all breeds, ranging from .32 to .47, while serving capacity and weights were phenotypically unrelated. Estimates of correlations between days to calving and weights were less consistent. Phenotypically, there was little association between the two traits. Genetic correlations for Zebu Crosses were negative and low to moderate (-.36 to -.66) while estimates for Angus were close to zero.