Five adult Merino and five adult Romney ewes with 7 months growth of fleece were subjected to nine different environmental challenges in a climate controlled room on consecutive days where the temperature humidity index (THI) was varied from 74.2 to 91.3 for up to 7 h at each exposure. Secretions were collected from glands in the skin on the back, midside and belly regions of each sheep. The sheep were shorn 5 months later. There was a significantly curvilinear increase in total skin gland output and the rate of secretion of titratable alkalinity and potassium ions with increasing THI. Romney sheep had a higher secretion rate than Merino sheep with no significant site effect. The rate of secretion of titratable alkalinity and potassium ions by the skin glands were both strongly related to tristimulus (Y-Z) of the fleece at shearing (base yellow) (R2 = 0.93, 0.92) and after incubation of the wool sample at 40°C and 100%RH for 6 d (challenge yellow) (R2 = 0.96, 0.95). These data indicate a particularly strong relationship between the rate of secretion of titratable alkalinity and potassium ions by the skin glands and the later propensity of the fleece to develop a yellow discolouration.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 286-292, 2004
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