Estimation of Variance Components by Sex and Theoretical Expectation and Selection Implication for Post Weaning Growth in Indigenous Cattle

Abstract

Weights of males and females cattle could be considered correlated or uncorrelated giving rise to homogeneity or heterogeneity of variance by sex. Variance components and heritability estimates were determined from pedigree records of YWT (YWT)(2177), composed of 923 males and  1254 female Tuli cattle born between 1983 and 1997, using the ASREML methodology. The direct additive variance was higher than maternal additive variance in both males and females. The maternal additive variance accounted for four and one percent of total phenotypic variance for males and females respectively, as compared to two percent in pooled data. The direct heritability estimate indicated low values for both males (0.15±0.001) and females (0.08±0.001), while maternal heritabilities were higher in males than females. The genetic correlation estimates between direct and maternal effects was low and positive in male and female combined data. The permanent environmental effects as proportion of the total phenotypic variance were less than one percent for both males and females. Total heritability estimates were low, 0.18 and 0.09 in males and females respectively, as compared with 0.27 in the pooled data. The high genetic correlation (0.89) between YWT in males and YWT in females indicated that YWT measured in different sex was the same trait hence splitting data by sex is unwarranted for purpose of genetic evaluation in this population. The maternal effects were not important for yearling in both males and females.