Implications

From estimates provided by state Departments of Agriculture, there are close to 1 million sheep that can have, or pass on, dark fibre or medullated fibre contamination.

Contamination Risk

Evidence from South Africa, WA and SA show that Merino ewes can be contaminated with coloured and/or medullated fibres during mating with these breeds, but more particularly when the crossbred lamb, growing coloured and/or medullated fibres is suckling its mother. It has been speculated that leaving a sufficient period between weaning of lambs and shearing of the Merino ewes could reduce the level of contaminant fibres to acceptable levels, but there is evidence also to show that this is not clear-cut.

Contamination in mixed flocks could occur from close contact of the 2 breeds in yards, races or pens.

At present, dark and medullated fibre contaminants are not measured prior to sale of the wool. Instead, reliance is placed on sheep breeding and management, clip preparation and wool marketing to assure low dark and medullated fibre risks or identify affected sale lots. Several examples of this are currently in place. In WA, the industry is asking growers to sign a declaration stating that the merino sheep from which a particular consignment was shorn have not had contact with exotic breeds. If no declaration is provided, the wool is suspected of potential contamination and the lots are sold in a separate tender catalogue. Nationally, the AWEX Code of Practice identifies a risk rating of 1 to 5 for sheep with contamination potential. Merino is 1 whilst the exotics are 5 and traditional coloured breeds, eg Suffolk, Southdown, Dorset are 3-4. The revised Wool Classer's specification has a section for nominating dark fibre risk and commenting where necessary. Wool Classers are required to stencil the suffix Y after the description on bales where they expect exotic sheep fibre contamination. The role of the woolclasser in handling wool where it is known that exotic breeds have been associated is a component of the Wool Classing Development Course now being conducted throughout Australia.

In South Africa, the biggest broker, BKB, has a distinguished brand "Fibre Care" where farmers guarantee that their clip is free from exotic sheep fibre contamination. Similarly, the National Wool Growers' Association, NWGA, has their own emblem "CCC" (Cape Clean Wool) with the same goals. The Wool Testing Bureau visually inspects Shirley Analysed webs for obvious contamination.

Identifying Contamination by Measurement

Until now most dark fibre contamination has been considered a discrete sampling problem, i.e. staples of stained or pigmented wool appear in a lot of wool but are not randomly dispersed through the wool. However, the contamination from exotic breeds is different. Each ewe fleece will have some contaminated fibres if mated or rearing a lamb from an exotic ram. Consequently, the core sample may be representative of the degree of contamination. Assuming this is so, what tests can be conducted?

Coefficient of Variation Differences

Preliminary observations from tests conducted in WA indicate that CVD may be useful for some breeds. Wesfarmers Dalgety have provided clip data to enable AWTA Ltd to identify possible trends. These are reported below;

This data shows that pure Awassi and Damara could be identified by a high CVD and this could be used to alert the broker to check the display sample. However, these pure breeds should be exhibiting enough colour to be obvious at time of sampling or when displayed. Compared to traditional XB or Merino lots, there is no distinguishing feature in the results to identify Awassi or Damara crosses. Even the percentage of fibres over 45 um doesn't help identification.

Ultra-violet Light

This has been tested on a web of fibres and found to be ineffective to detect either pigmented or medullated fibres. Ortho-dichlorobenzene This traditional technique is used to identify the presence of medullated fibres. It relies on the chemical having a similar refractive index to wool. It is not a quantitative test.

CSIRO Dark Fibre Detector

This has been tested on a web of fibres and found to be able to identify dark fibres. However, the process is manual, slow and unreliable.

OFDA

This able to measure medullation. Its ability to identify a coloured fibre is unknown.

Optalyser

This instrument, developed by Centexbel, can measure coloured fibres, VM specs and neps in combed sliver. Its application to raw wool is unknown. The machine is expensive and would probably require a raw wool sample to be prepared into a sliver for measurement.

Conclusion

It is clear from the above that there is no easy solution to the detection or measurement of dark and/or medullated fibres. While AWTA Ltd is examining these alternatives, some review of modern image and colour measurement technology may be a useful step forward. However, we see no quick fix.

Meanwhile, the industry must address the issue via the management and classing practices being put in place in conjunction with Classer and Grower declarations.

Acknowledgements

Information for this Status Report has been obtained from the Departments of Agriculture, or equivalent, in each mainland state. Photos were drawn from the Oklahoma State University website. Particular thanks go to the research and commentary of Malcolm Fleet and his colleagues at the South Australian Research and Development Institute.

The assistance of Ron Myers (Wesfarmers/Dalgety - WA) in providing clip information and samples used for examining CVD differences is also acknowledged.

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