Influence of sex on genetic expressions and variance of 4-month weight of Swedish lambs

Influence of sex on 4-month weight was studied on lambs in the Swedish Sheep Recording Scheme (SSRS). Correlations between genetic expressions in the sexes were of interest and 4-month weight was analysed as a different trait in female and male lambs. Data included two sets of breeds, the so-called white breeds (Swedish landrace breeds, Texel, Dorset, Oxford down, Suffolk, East Friesian milk. sheep, and Swedish crossbred; (23,985 observations) and the Gotland breed (35,891 observations)). Phenotypic variances were lower for females than for males. Estimates of direct heritabilities (0.14 - 0.24) were higher, whereas maternal heritabilities (0.07-0.18) were lower for females. Negative genetic correlations between direct and maternal effects (-0.45 to -0.19) were more pronounced for males. The results indicate. heterogeneity of both genetic and environmental variances by sex. Interactions between sex and lamb age on weight were also shown. Genetic correlations between direct effects on the female and male traits, respectively, and the corresponding correlations between maternal effects were high (0.89 - 0.99). It is concluded that the observed heterogeneity in variance due to sex could be accounted for in the genetic evaluations by treating 4-month weight as a different trait in female and male lambs. (C) 2003 Elsevier B.V. All rights reserved.