Prediction and predisposition of sheep to fleece rot

Abstract

Fleece rot is a bacterial skin condition that commonly occurs in fine woolled sheep. It can cause permanent fleece discolouration, and make an animal more susceptible to body strike by blowflies. Production losses are incurred due to reduced wool quality and poor stock health. One thousand sheep on three properties were monitored for fleece rot development in each of two years. Mid-side wool samples were collected and measured for effective wool colour, fibre diameter (mean and variability) and yield in October/November each year. Greasy wool colour was assessed on the samples and later on the sheep. Fleece rot, developed under natural conditions on-farm, was assessed at the end of the following year (October/November), and scored for incidence and severity. The fleece characteristics were analysed to investigate the predictive correlations with fleece rot incidence and severity. Liability to fleece rot was calculated by transforming the incidence dependent correlations to a normally distributed scale of liability. There was a high incidence of fleece rot on all properties in both years. The severity of fleece rot increased as the incidence increased within properties, in both years. There was a very low incidence of body strike. A wide range of effective colours were found. The majority of the samples were within the susceptible to discolouration range, with few in the resistant range. The range of fibre diameter and yield measured within all trial mobs was small. The greasy wool colour assessed on the sheep was very highly significantly correlated (P>=0.001) with fleece rot incidence, severity, and liability to fleece rot on all properties. The greasy sample colour and the effective colour was significantly (P>0.05) to highly significantly (P>0.01) correlated to fleece rot incidence and severity in some years. The variation in fibre diameter and yield did not explain any of the variation in fleece rot incidence or severity. The results for individual properties suggested that some effective colour measurements and fibre diameter statistics could be utilised in predicting liability to fleece rot. The proportion of the variability in fleece rot incidence, severity and liability explained by the effective colour assessments and measurements suggested that the incubation procedures were not indicative of the processes occurring within the fleece as fleece rot develops. The colour of the greasy wool was the greatest value in predicting predisposition to fleece rot.