A comparison of the topmaking performance of wool from sheep selected by index and visual methods

The topmaking performance of fleeces from sheep that were ranked high or lo w on index selection using objective measurement was compared with that of sheep from the same flock that were ranked high or low on visual assessment . A flock of 451 15-month-old fine-wool Merino sheep were classed by 2 experi enced fine-wool sheep classers into 3 grades: best, average and culls. Fort y-four sheep were assessed as 'best' and 77 sheep were graded as 'culls' by both classers. These sheep were defined as the 'best visual' and 'worst vi sual' sheep, respectively. Measurements of clean fleece weight, mean fibre diameter, coefficient of variation of fibre diameter and body weight were u sed in a selection index to rank all sheep in the flock. The selection inde x was designed to rapidly reduce mean fibre diameter and slowly increase cl ean fleece weight, whilst maintaining staple strength and body weight. The 44 sheep with the highest index value were defined as 'best index' sheep an d the group Of 77 sheep with the lowest index or obvious physical faults we re defined as the 'worst index' sheep. Twenty-five fleeces were randomly se lected from each of the 'best' and 'worst visual', 'best' and 'worst index' sheep for individual processing through to top. The fleeces from the 'best index' sheep produced greater quantities of tops that were significantly finer, longer, of lower curvature and produced les s noll than all other groups. In contrast to the large difference in qualit y between tops from the 'best' and 'worst index' sheep, there was little di fference in quality between tops from the 'best' and 'worst visual' sheep. This indicates that the traditional wool producer views of wool quality are unrelated to processing performance. It was concluded that Merino sheep se lected by index selection using direct measurement of fleece weight, mean f ibre diameter and coefficient of variation of diameter as selection criteri a produced greater quantities of wool of superior processing performance to that from sheep selected using visual assessment.