Wool was collected from five sheep with a propensity for wool yellowing. Sub-samples, from which the wool tip had been removed, were cut into 2cm lengths and incubated at 40°C for 6 days to provide an environment conducive to wool yellowing (YCT).Five treatments were applied to sub-samples of each fleece prior to YCT. Four sub-samples were gamma irradiated in an attempt to kill all bacteria present on the fleece (-B), the remaining subsample was not irradiated. Two -B sub-samples were re-inoculated with bacteria collected from the original fleece samples (+B). Each of the +B and -B samples was then either incubated at 0% humidity (-H) or 100% humidity (+H) for the YCT. Wool yellowness (Y-Z) was measured before and after YCT using standard methods. No relationship was apparent between the number of bacterial colonies in the original fleece (plated onto nutrient agar), and the pre-YCT Y-Z (R2=0.20; P=0.06), Y-Z after the YCT (R2=0.19; P=0.06), or the change in wool Y-Z during the YCT (R2=0.07; P=0.27). Gamma irradiation eliminated bacteria from the wool samples but increased their Y-Z pre-YCT (mean ± S.D, non-irradiated 2.46±0.55; irradiated 4.35±0.43; P<0.001). Discolouration of wool (Y-Z) was increased by humidity during YCT (-H 1.06±0.45, +H 4.96±1.46; P<0.001). At 100% humidity, reinoculation with bacteria increased wool Y-Z during YCT (+B 6.13±0.87; -B 3.78±0.75; P<0.01). This effect of reinoculation was lost at 0% humidity. The interaction between humidity and reinoculation was significant (P<0.05). This study supports the hypothesis that bacteria are involved in the yellow discolouration of wool in the presence of high humidity.

L, Winder, K Baronian, J Webber, and B Muller

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 277-280, 1998
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