Effect of sample preparation method on the validity of an early-life predictor of hogget wool bulk in genotypes used to develop GrowBulk sheep

Selection for wool bulk is normally undertaken in yearlings. In this study, a mixed-sex group of 170 GrowBulk sheep were wool sampled at 6 and 12 months of age. Measurements of fibre curvature and fibre diameter following degreasing a wool sample taken at 6 months of age with either water or solvent, explained 69% and 67% respectively of the variation in core bulk at 12 months of age. A combination of fibre curvature and fibre diameter measured following degreasing by either method was equally effective in predicting core bulk at 12 months of age. Precision of the predicted core bulk values was equivalent to direct core bulk measurement. Early-life prediction of core bulk from measurements of fibre curvature and fibre diameter taken close to the skin using consistent sample preparation methods, is a low-cost objective procedure to rank sheep for culling young sheep on wool bulk.