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