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Bah Bah White Sheep?

Is wool on white sheep always white? Not all the time. Yellow colour can form in wool under certain environmental conditions, causing a major problem for the industry.

Yellow wool can't be dyed pale colours unless it has extra processing. Farmers get less money for yellow wool, and wool processors need to spend money bleaching it before dyeing, which can damage the fibres and may not be permanent. Colour affects wool from all breeds but has the greatest financial implications for the fine and half-bred wools used in the apparel industry.

Dr Peter Maher and Dr Bagda Benavides from Lincoln University are studying Corriedale sheep, taking colour measurements of the wool before processing and applying statistical tests to find out how much was succeptible to developing yellow stain. Their results showed that in the fleeces tested 82% of the sheep had the potential to develop yellow stain.

"It might seem really simple to select against breeding from these sheep in the future," says Maher, "but unfortunately it's not as easy as that. Sheep only show yellow stains in their wool under moist and warm conditions, so sheep in a flock may not show any yellow colour one year but develop colour the next. It partly depends on the weather."

"However, even after finding ways of predicting which sheep are succeptible to yellowing, it was found that white wool sheep tended to have lower fleece weight. This shows the genes involved in expressing wool colour are linked to other genes as well. This is a common occurrence, but it does leave people trying to improve wool colour with a financial dilemma."

"Farmers who decide to select sheep to improve the wool colour of their flocks will risk a reduction in their total wool clip. The result of our work shows which of the measurements taken are the most useful for changing wool colour. A sensible option for farmers is to select their flocks so that the wool colour does not deteriorate, but this will reduce fleece weight gains," says Maher.

"In an ideal world the wool buyers would pay a premium for white wool such that it would be an economic advantage for the farmers to improve the colour of their flocks, but this has not happened yet. The results are available however for anybody who does decide to take the risk."

Researchers are looking for specific genetic markers that can be used to predict wool colour. If they are found, the selection process for breeding will be much more certain as this work has the potential to allow improvements in colour to be made without losses in fleece weight.