Regional Distribution of Medullated Fibres in Merino Fleeces and Relationship with Birth Coat Halo-hair

Abstract

Problems arising in wool processing from medullated fibres in Merino wool has recently become an issue, primarily due to crossbreeding with highly medullated meat sheep breed types. Since medullation forms a minor component of Merino wool, metrology research has to determine thresholds in raw wool that coincide with potential faults in fabric. This study reports on the application of OFDA100 and the AWTA Ltd. tests for measuring medullated fibre in wool. These results are used to show variation in fleeces between 3 body sites (mid-side, mid-dorsal neck and central lower leg) and the relationships of medullated fibres with halo-hairs visible on the Merino lambÂ’s birth coat. The rear leg wool sample had the highest concentration of medullated fibres although the dorsal, neck site had higher concentrations of short medullation (3-10mm) and flat medullated fibres than the midside. Medullated fibre content at the second shearing (16-months of age) was associated with higher levels of halo-hairs in the birth coat. Lambs showing halo-hair can be relatively common within Merino flocks so the question remains whether direct selection against this feature is warranted. A wider and more detailed investigation using industry Merino flocks, together with processing evaluation, is required to determine the merit of selecting against the presence of halo-hair on Merino lambs and/or measured medullated fibre.