Genetic parameters for growth of young dual purpose Simmental bulls using random regression

Additive genetic and permanent environment covariance functions and corresponding heritabilities and correlations were estimated for weight, height at withers, body length and heart girth of young dual purpose Simmental bulls. Data consisted of 11, 890 records of 1, 385 bulls born from 1974 to 2002. The pedigree file consisted of 3, 274 animals. The bulls were raised in the performance test station at Varazdin, Croatia. Measurements were taken from 100 to 400 d of age, approximately once per month. Covariance functions were estimated by using polynomial random regression. Interaction of year x season and quadratic regression on age were defined as fixed effects, while animal and permanent environment due to measurements on the same bull were defined as random effects. Polynomials of order three to five were adequate in estimating covariance functions. Estimated heritabilities ranged from 0.36 to 0.54 for weight, from 0.20 to 0.50 for height at withers, from 0.20 to 0.58 for body length, and from 0.31 to 0.60 for heart girth. Genetic correlations between longitudinal records ranged from 0.71 to 0.99, and phenotypic correlations ranged from 0.39 to 0.97. The correlations declined as days between measurements increased. The estimated covariance functions from this study demonstrated heterogeneity of covariances of body measurements in young Simmental bulls implicating random regression as an appropriate method for estimating genetic parameters and breeding values. Thus, random regression should be used in procedures for genetic evaluation of growth traits in dual purpose Simmental cattle.