THE SIGNIFICANCE OF CERTAIN SKIN CHARACTERS OF SHEEP IN RESISTANCE AND SUSCEPTIBILITY TO FLEECE-ROT AND BODY STRIKE

Micro-anatomical differences in skin structure associated with resistance and susceptibility of sheep to fleece-rot and body strike were identified, and found to be of similar magnitude in 2 genetically divergent flocks of medium-woolled Merino ewes. Susceptible sheep were characterised by smaller follicle groups, resulting in higher densities of follicle populations with greater concentrations of the primary follicles (and sudoriferous glands) than in the resistant sheep. From these smaller follicle groups of susceptible sheep, thicker wool fibres grew than were found in the resistant sheep.
The significance of these findings is discussed in relation to the pathogenesis of fleece-rot and body strike of sheep, and the value of the measured skin characters as a method for identifying resistant sheep.     

THE CHANGES IN PROTEIN CONCENTRATION AND BACTERIA OF FLEECE AND SKIN DURING THE DEVELOPMENT OF FLEECE-ROT AND BODY STRIKE IN SHEEP

The sequence of events in the development of fleece-rot and body strike in sheep is described. When sheep were wetted by rain, vast increases in the numbers on microorganisms on the fleece and skin surface occured. Frequently, only one bacterial genus, Pseudomonas, proliferated and produced a bacteriostat to inhibit the growth of other resident flora. The development of fleece-rot lesions was characterised by a sudden substantial increase od soluble protein, presumably plasma protein, onto the skin surface. Pseudomonas spp proliferated on the skin surface and frequently produced extracellular, green pigment. First instar blowfly larvae were observed subsequently in such lesions.     

AN IN-VITRO TECHNIQUE FOR STUDYING FLEECE-ROT AND FLY STRIKE IN SHEEP

Fleece-rot was experimentally induced in-vitro by wetting and incubating Merino wool samples embedded in serum-agar. Gravid Lucilia cuprina were readily-attracted to these wool culture plates to oviposit. Where serum was freely available to newly-hatched larvae, fly strike and larval development ensued. Using this technique, fleece-rot and oviposition were found to be markedly influenced by the availability of protein and by bacterial activity, particularly that of Pseudomonas spp. The results indicated that odours emanating from wool culture plates containing the latter species played an important role in oviposition. Furthermore, these events varied according to the type of fleece selected, and could be prevented by the addition of a bactericide.     

THE COMPARATIVE SENSITIVITY OF SHEEP AND CHICKEN EMBRYOS TO BLUETONGUE VIRUS AND OBSERVATIONS ON VIRAEMIA IN EXPERIMENTALLY INFECTED SHEEP

The virus titre in sheep blood samples received from BT-suspected cases in the field was assayed in sheep and in chicken embryos. These infected blood samples represented 3 different BT virus types: 4, 10 and 16. Three identical experiments were performed, one with each of the 3 different virus types. Ten-fold dilutions of the infected blood samples were prepared and 1 ml of each blood dilution was inoculated IV into series of 10 to 12-month old susceptible sheep; at the same time 0.1 ml of each dilution was inoculated IV into series of 10 to 13-day-old chicken embryos. The virus titre was found to be similar when assayed in the two host systems. There was no correlation between the amount of virus inoculated and the severity of symptoms in the inoculated sheep. The virus content in daily blood samples collected from the experimental sheep was assayed by IV inoculation of CE. Virus was isolated from all the reacting sheep and was detected sometimes as early as 1 day PI and as late as 30 days PI. A high titre of log10 4.0 to 7.0 per 1 ml of blood was recorded during several consecutive days before and after the onset of clinical signs. There seemed to be an inverse ratio between the amount of virus inoculated and the number of days the virus persisted in the bloodstream. The neutralisation index in day 22 serum samples was 3.5 to 4.5. Virus was isolated from some of the reacting sheep on the day that these antibody levels were recorded. Since the comparative simultaneous titrations of BT virus in sheep and in CE yielded similar results, the IV inoculation of CE is advocated as the routine method to be employed for laboratory diagnosis of this disease.