Selection for economic characters in Australian Merino sheep.

Abstract

The effect of inbreeding and parent-offspring regressions for some economic characters of Merino sheep were estimated by a least-squares procedure. The model was:

Y_i = a + b₁X_1i + b₂X_2i + e_i ,

where Y_i and X_1i represent the phenotype and coefficient of inbreeding of the ith sheep, X_2i the phenotype of the dam of that sheep, and e_i the random deviation of Y, from its expected value. Increased coefficients of inbreeding were accompanied by highly significant decreases in greasy and clean fleece weights, body weight, and fold score. No significant association was observed between inbreeding and yield, staple length, crimps per inch, or birthcoat grading. Increased inbreeding was associated with decreased survival. Significant correlations between X₁ and X₂ were demonstrated for fleece weights, staple length, body weight, and crimps per inch. The implications of these correlations are discussed. The parent-offspring regressions were all highly significant. Estimates of heritability were high for all characters studied. The importance of these findings on the effectiveness of selection for flock improvement is considered.