Estimating the association between wool and skin characters and fleece rot

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Abstract
To assess the value of skin and fleece characters as potential indirect selection criteria for increased resistance to fleece rot, estimates of the genetic correlations between the skin and fleece characters and fleece rot are needed. The characters most likely to be useful can be identified relatively cheaply and quickly by estimating the phenotypic correlation with fleece rot. This paper illustrates how phenotypic correlations with fleece rot, scored as an all-or-none character, can be estimated retrospectively from published estimates of means and standard deviations of fleece and skin characters measured in groups of sheep affected by or free from fleece rot. The paper emphasizes the incidence-dependent nature of the correlation coefficient so obtained, and points out that this must be allowed for when comparisons of correlations are made between flocks in which the incidence of fleece rot differs. This problem can be avoided by using the concept of liability to fleece rot. Data from three recently published papers are used to illustrate the main points.