Four two-year-old Romney ewes born in the Waikato and four two-year-old Romney ewes born in Canterbury that had been grazed together in the Waikato for 12 months, were used to investigate aspects of yellowing in wool samples grown on the mid-back, mid-side and mid-belly. Two sheep in each sub-group had a history of having a relatively high and two sheep a relatively low, propensity for their fleece to turn yellow during the previous year. Dimensional fibre characteristics, with the exception of staple length, were not significantly different between body sites, between the propensity groups or between birth farm groups. Wool was shorter on the belly than on the other two sites. Incubating greasy sub-samples of each fleece at 40°C and 100% relative humidity for 6 d induced a curvilinear increase in yellowness with the CIE Y - Z value approaching an asymptote. A significant amount of the variation in yellowing was explained by the concentration of K, Ca and possibly Na, elements secreted in the suint. These data suggest that the propensity of a fleece to turn yellow is not related to fleece architecture or the elemental composition of the fibres, but may have a physiological basis possibly related to sweating behaviour.
Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 61-64, 2002
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