Objectives & Summary

Objectives

• To examine the detection rates by SARDI and AWTA Ltd of Dark and Medullated Fibres from Sale Lot core samples of Merino wools with a known history of contact with Damara sheep.
• To record the times taken to perform the test as a basis for determining the cost of any future Dark Fibre testing by AWTA Ltd.

Summary

• This fact sheet reports on a trial designed by AWTA Ltd, using a technique developed by SARDI (South Australian Research & Development Institute) based on the CSIRO dark fibre detector, to assess levels of Dark Fibre contamination in core samples from sale lots of wool from merino ewes known to have been in contact with Damara rams. This assessment was replicated by SARDI.
• The sale lots were separated into two groups. The first consisted of dry ewes that had been in contact with the Damara rams for 6 weeks, then drafted off and shorn separately from the main shearing. These were run into the shearing shed using a new system that ensures that there is minimal risk of contamination from the yards and races. The second consisted of wet ewes, in contact with the rams for the same period, with the lambs at foot for 18 weeks. The lambs were separated from their mothers 6 weeks prior to shearing. A control group of sale lots, from sheep known not to have been in contact with Damara Rams or Damara crossbred lambs was also included.
• The examinations showed that despite the subjective nature of the measurement technique, AWTA Ltd and SARDI were clearly able to separate wools expected to have no contamination from wools likely to have heavy contamination. Although the wool from the dry ewes tended to be less contaminated than that from the wet ewes, contamination of both groups was unacceptably high.
• It is technically feasible for AWTA Ltd to provide guidance about the level of Dark Fibre contamination (i.e. whether or not any contamination is present) in Merino Fleece wool after contact with Damara, and possibly other exotic, sheep using an adaptation of the technique developed by SARDI.
• However, it is not commercially feasible to routinely provide this service for all presale lots, or even a significant subset of all presale lots, given the labour input required.
• The guidance test technique is based, to a significant extent, on the subjective judgment of operators. There was considerable difference between the AWTA Ltd and SARDI Dark Fibre counts for individual samples. However, both laboratories have clearly separated wools expected to have no contamination from wools expected to have heavy contamination.
• Given that in such instances the contamination is distributed throughout the fleece it should be technically feasible, given sufficient commitment of funds, to develop a commercial screening test.