Studies in fleece-rot of sheep.

Abstract

Occasions of unduly heavy and prolonged rainfall during the period April 1946 – July 1951 resulted in the occurrence of fleece-rot in sheep of the Field Station flock in each of the six years. Data obtained from periodic examinations of the flock have been related to the nature of climatic conditions associated with outbreaks of the disease. They show that when rain occurs in falls of sufficient intensity and frequency to wet sheep to the skin for a period of a week or more, fleece-rot may be expected to develop in some of them. The longer the period for which the sheep are kept wet, the greater the number in a flock which will be affected. Fleece-rot was experimentally induced in four out of five Merino sheep known to be susceptible to the condition, whereas five animals known to be resistant were unaffected by the same treatment. Microscopic examination of skin sections taken from naturally occurring cases revealed the presence of a dermatitis. A similar condition was observed in skin sections from the animals in which fleece-rot was experimentally induced. Young sheep were found to be more susceptible than old. There was no association between degree of wrinkling and susceptibility or between 'grip' and susceptibility. When subjectively-appraised attributes of the fleece were related to the occurrence of fleece-rot, confusing results were obtained. However, when measured fleece data, obtained from a group of Merino sheep which had been under observation for four consecutive years, were considered, it was found that those for clean-scoured yield, wax and suint ratio, and density of fibre population per unit area of skin surface, were related to resistance or susceptibility. Nevertheless, a number of animals were found which were susceptible or resistant to the disease despite the nature of their fleece attributes. Differences in susceptibility were found between families of Merino sheep. These are associated with between-family differences for the fleece attributes found to be important in fleece-rot reaction.

The fleece as a habitat for micro-organisms

“…The names dry yolk, cakey yolk, hard yolk also refer to this condition as seen in the non-active nhase after drying-out of the fleece. Hayman (1953Hayman ( , 1955 has agreed with Belschner and Seddon's earlier contention that this condition is brought abou~ by the action of bacteria on a serous exudate of the skin. This author also found that a predisposing factor in the formation of the exudate was a plentiful sunply of moisture.…”

“…to skin level and have little or no effect on the growth of micro-organisms and, even after heavy rain, the rapid drying out of the fleece (Fraser, 1957) limits the time available for active microbial growth and multiplication. The work of Hayman (1953) and Henderson (1955) has shown that sheep can be divided into two groups, those which are susceptible to bacterial discoloration of the wool and the growth of micro-organisms at the base of the fleece generally, and those which are resistant. Although the resistant and susceptible types of wool may be easily separated by subjective appraisal by an experienced wool man, the chemical orphysical bases for this separation are not known.…”

On-farm factors affecting physical quality of Merino wool. 1. Nutrition, reproduction, health and management

“…In many districts in New South Wales, Australia, (NSW) the average prevalence of fleece rot in yearlings is ∼ 25% pa and is greater in yearlings than adult sheep. Many of the organisms involved in fleece rot produce a pigment, typically bright green but also blue, orange, brown or pink (Hayman, 1953;Fraser and Mulcock, 1956). Some of this discolouration is nonscourable and results in price discounts due to colour.…”

The Digestion of Wool by a Keratinolytic Bacillus

“…It is characterized by superficial *The pH of the contents of a cyst containing disrupted wool measured at 8, 13, 24, and 36 weeks ranged from 6·8 to 8·0. dermatitis and a serous exudate which on drying causes matting of the wool fibres (Hayman 1953). The affected wool becomes hard and stringy and in severe cases may be easily plucked from abnormal areas of skin.…”

“…The causative organism was an aerobic, mesophilic, spore-forming rod, and was capable of breaking wool into individual cells in vitro. Hayman (1953), in producing fleece rot experimentally, mentions a pink coloration and rotting which developed after incubating moist wool for 3 weeks. No mention is made of a causative organism.…”