Genetic aspects of greasy wool colour assessments in Merino sheep

Abstract

\"Wool colour is an important determinant of wool price, especially in fine and superfine Merinos. While objective measurement is not routinely available on farm many Merino breeders subjectively score sheep on greasy wool colour on farm for selection purposes. This study examines subjective greasy wool colour scores from an industry data set. Wool colour scores ranged from 1 to 5, with a score of 1 being superior (whiter) to a score of 5. Age and birth type significantly affected greasy wool colour scores. Older sheep had lower colour scores (whiter wool) and multiple born lambs had lower scores than singles. Greasy wool colour, scored in the yards and wool shed, are moderately heritable, 0.35 and 0.31, respectively. Both greasy wool colour scores also had a small but significant maternal genetic heritability of 0.03. Sheep with higher body weight (rg=0.21 to 0.23) and greasy fleece weight (rg=0.29 to 0.34) had more greasy wool colour. Greasy wool colour assessed at shearing in the wool shed was negatively genetically correlated with fat depth (rg=-0.39) and mean fibre curvature (rg=-0.22). The remaining traits examined in this study were not significantly correlated with greasy wool colour scores. The correlations involving these other traits indicate that wool colour can be improved genetically without detrimental effects to these other traits. Greasy wool colour assessed in the yards is the same trait genetically (rg=0.94) as that assessed at shearing in the wool shed. Wool colour scores recorded across ages are highly correlated indicating that from a breeding program point of view wool colour only needs to be measured at one time throughout an animalÂ’s life. Greasy wool colour is moderately repeatable (0.46) and therefore will respond to selection.\"