What is Dark and Medullated Fibre Contamination?

Medullated Fibres

Medullated fibres are characterised by a medulla or a hollow core. This may extend for a considerable length along the fibre or may consist of a number of discrete hollow areas along the fibre. Medullated fibres appear chalky because light is reflected from the inner wall.  They are a problem in fabrics because their dye update is different from non-medullated fibres and as a consequence they cause a visible defect in the fabric.

The degree of medullation is usually characterised by estimating the percentage of the fibre occupied by the hollow medulla.

Types of medulla that can occur in wool fibres are (a) fragmental, (b) interrupted and (c) continuous

Dark & Pigmented Fibres

Dark and Pigmented fibres occur in all sheep, but generally in well bred white merino sheep the numbers are very low. The colour of the fibre is caused by a chemical called melanin, produced by cells called melanocytes in the skin of the sheep.  The genes controlling melanin production are able to regulate pigmentation in white Merino sheep, at least in part, by controlling the location and activity of melanocytes within the wool-bearing skin.  However, the gene responsible for active melanin production is not absent - it is recessive. Consequently white merinos can produce lambs with pigmented patches.  Part of the animal husbandry practices of Australian Merino wool produces is to cull such lambs from their flocks.

Pigmentation can also be produced by fecal or urine stains, particularly around the breech of the sheep. Management of this type of stain involves crutching sheep before shearing.

Dark, pigmented and urine stained fibres also cause fabric defects as they take dye differently from non-pigmented or stained fibres.