Fleece samples were taken from the back, side and belly of three adult ewes in one Merino flock and three adult ewes in one Romney flock in each of six regions of New Zealand (Waikato, Manawatu, Wairarapa, Marlborough, Canterbury, Otago). Each fleece was 12 months growth. These samples were used to compare factors associated with wool yellowing as measured by tristimulus (Y-Z) values. Neither the region of New Zealand where the sheep grazed nor the measured dimensional fleece characteristics, were related to fleece yellowing. The pH of an aqueous extract of greasy wool was strongly related (R2 = 0.93) to tristimulus (Y-Z) (base yellow) at shearing but less strongly related (R2 = 0.70) to tristimulus (Y-Z) after the sample had been incubated at 40°C and 100% RH for 6 d. Merino samples had a lower tristimulus (Y-Z), both before and after incubation, at a particular pH than Romney samples. Back wool did not increase in yellowness as much during incubation as side or belly wool possibly on account of photo-oxidation following prolonged exposure to sunlight. These data indicate a close relationship between pH of a water soluble component of greasy wool and the extent of wool yellowing that was influenced by sheep breed and body site.

RMW, Sumner, SR Young, and MP Upsdell

Proceedings of the New Zealand Society of Animal Production, Volume 63, Queenstown, 155-159, 2003
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