Heritability of Birth Weight and Its Relationship with Production in Dairy Cattle

Abstract

The data included in this study were taken from the University of Illinois dairy herd and consisted of 1234 birth weights representing the five major breeds of dairy cattle. A comparison of the confidence intervals demonstrates significant breed differences at the 0.001 level of probability for all possible comparisons. The fixed effects of sex of calf and calving sequence were estimated by the method of least-squares. These combined effects were found to be significant at the 0.01 level of probability in all five breeds. Adjustment factors so obtained were applied to birth weights before the estimates of heritability and genetic correlations were derived. Pooled within-breed estimates of heritability of birth weight obtained by multiplying, respectively, by 4, 2, and 2, paternal half-sib correlation, intra-sire regression of offpsring on dam, and full-sib correlation were 0.38, 0.48, and 0.51. Theoretically, it should be relatively easy to change the average birth weight of a population. The absence of correlations significantly different from zero indicated that birth weight of the calf and immediately subsequent lactation production of the dam were essentially independent. Intra-service-sire correlations between birth weight of a calf and its subsequent production were not significantly different from zero in any of the five breeds or for a within-breed pooled estimate. The pooled within-breed estimates of the genetic correlations between birth weight and milk and fat productions were small and not significantly different from zero. It appears that birth weight and production are genetically independent.