Fleece rot and body strike in Merino sheep. III. Significance of fleece moisture following experimental induction of fleece rot

Abstract

The relationship between fleece wetting and drying characteristics and liability of sheep to fleece rot and body strike was examined following experimental wetting. The liability of sheep to fleece rot was reflected by both wetting and drying characteristics. Wetness of the fleece was estimated gravimetrically and was found to be a simple, fast and relatively robust technique. Moisture increased from 13% in the dry fleece up to 123% at skin level in sheep exposed from 0 to 10 days' wetting. Consistent differences were reported in proximal and full staple moisture levels between sheep affected and unaffected with fleece rot or body strike. Drying characteristics of individual sheep were recorded by means of an electronic hygrometer in sheep up to 5 days after wetting. A lag phase in the drying of sheep susceptible to fleece rot or bodystrike was recorded, compared with resistant sheep. The most resistant sheep showed a slightly concave drying curve (-12.4% R.H. day-1 + 0.06% R.H. day-2) after wetting, whereas the most susceptible sheep showed a slightly convex drying curve (- 11.4% R.H. day-1 0.05% R.H. day-2). The maximum difference in fleece relative humidity between the two groups of sheep occurred between 1 and 3 days after wetting. Measurement of fleece relative humidity before wetting in the dry fleece, did not predict the liability of sheep to fleece rot and body strike.Moisture levels in the fleece during and immediately following wetting accounted for differences in fleece rot due to experimental treatments and genetic flock differences. Based on a single full-staple moisture measurement of 945 sheep, representing the progeny of 134 sires, the heritability of fleece moisture was 0.28 ¦ 0.12 and had a genetic correlation with fleece rot incidence and severity of 0.74 ¦ 0.24 and 0.79 ¦ 0.19 respectively. Further work should identify fleece components which affect the wetting and drying characteristics of the fleece during the development of fleece rot.