Estimates of relationship between milk yield and age at first calving in cattle using multivariate REML

Abstract

Relationship between milk yield and age at first calving in cattle were calculated from (co) variances estimated by multivariate restricted maximum likelihood with equal design matrix fitting a unbalanced mixed model with herd, year and calendar month of calving as fixed effects, and sire and residual errors as independent random effects. Univariate analyses were also carried out to compare the variances estimated by multivariate analysis. The data consisted of first lactation records on 733 purebred progeny of 69 Hariana sires in 3 herds from 1969 to 1981. The genetic correlation between yield and age was estimated to be 0.82+0.07 or 0.82-0.07, but the phenotypic correlation was only 0.37+0.05 or 0.37-0.05. Large differences were observed in the estimates of variances for milk yield from univariate and multivariate analysis, but for age at first calving the variances were quite similar.