A predictive test for susceptibility to fleece yellowing, which has a high heritability (0.5), is described. In a flock of Corriedale ewes 2 lines, selected entirely on the basis of the predictive test, demonstrated predicted levels of fleece yellowness when conditions promoted high levels of discoloration. Assessed greasy and measured scoured wool yellowness were not highly correlated. The yellowness value of scoured wool of highly resistant (HR) fleeces was always low; that of highly susceptible (HS) fleeces was variable and often high. The yellowness value of HS fleeces increased on storage of greasy fleeces. There was a negative correlation between yield and susceptibility, which was not strong enough to use for predictive purposes. HR and HS Corriedale ewes, thoroughly washed and then housed to eliminate weather effects, showed striking differences in yield % (83 v 61), wax % (16 v 25) and suint % (5 v 29) respectively. Pilocarpine hydrochloride was administered to the housed sheep to determine whether fleece yellowing and related faults were caused by excessive sweating. Results are variable.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 197, 1985
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