Wool scoured colour: Heritability, genetic and phenotypic correlations with wool traits in Corriedale sheep

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Scoured wool colour determines the potenti al colour range and dye-ability of wool tops. Improvement of scoured wool colour of fleeces from Corriedale sheep through multi-trait breeding programmes is currently not possible due to limited existing information on its heritability and genetic correlations with other fleece traits. The present study aimed to determine genetic parameters of scoured wool colour traits, with emphasis on their genetic and phenotypic correlations with objectively and visually assessed fleece traits. Data from 1181 hoggets of two experimental flocks were used. Heritabilities were estimated for scoured wool yellowness (Y-Z) and scoured wool brightness (Y), greasy fleece weight (GFW) and clean fleece weight (CFW), wool yield (WY), mean fibre diameter (MFD), coefficient of variation of fibre diameter (CVD), staple length (SL), staple strength (SS) and a range of visual wool traits (greasy wool colour, wool character, handle, staple formation, dust penetration and cross-linking). Trivariate statistical models under a Bayesian setting were used, including the environmental effects of flock, sex, litter size and climatic variables (accumulated precipitation, maximum temperature and relative humidity) and the animal genetic effect, Y-Z was moderately heritable (0.22 ± 0.06) and should respond to selection. Its genetic correlations with GFW, CFW and SL were significant, positive (unfavourable) and moderate (0.43 ± 0.15, 0.56 ± 0.14, and 0.44 ± 0.14, respectively). There was a positive (favourable) association between MFD and Y-Z (0.25 ± 0.17). The genetic correlation between Y-Z and greasy wool colour was 0.70 ± 0.13, although this trait showed a low heritability value (0.13 ± 0.04). Wool brightness showed low heritability (0.10 ± 0.04) and only appeared to be genetically correlated with SL and wool character (0.56 ± 0.17 and 0.39 ± 0.22, respectively). Phenotypic correlations of Y-Z and Y with wool production and quality traits were all less than 0.20 in size. Overall, this study reports new genetic parameters for wool colour and their associations with fleece traits in Corriedale sheep. Our findings suggest that it could be possible to select against wool yellowness, with some caution, given the possible detrimental effects on economically important wool traits, especially fleece weight and staple length. More investigation is warranted. Indirect selection via greasy wool colour is an alternative approach, but the responses would be slower. Easy and cheap measurement should be balanced against the size of the response from direct selection versus indirect selection.