Anthelmintic resistance and sheep management practices in south western Victoria.

Twenty-eight farms in 7 shires in south western Victoria were selected and tested for presence of benzimidazole-resistant nematodes between November 1979 and June 1981. Mean faecal egg counts of sheep were less than 100 strongyloid eggs/g on 11 farms. Faecal egg count reduction tests were conducted on the remaining 17 farms and thiabendazole was less than 90% efficient in reducing egg counts in sheep from 5 (29%) of these farms. Thiabendazole-resistant Teladorsagia circumcincta were identified at necropsy of experimentally infected treated sheep. In further studies a survey of 104 farms was conducted in the Mount Rouse and Dundas shires of western Victoria in 1981 and 1982 respectively to determine the prevalence of anthelmintic resistance in these shires. Mean faecal egg counts among weaner sheep in the winter-spring of both years were less than 100 eggs/g which indicated low levels of parasitic nematode populations. A faecal egg count reduction test was conducted on 10 farms and thiabendazole was less than 90% efficient on 3; levamisole was greater than 90% efficient in all 10 tests. Most of the surveyed farms carried Merino or Merino crossbred sheep at 10 to 15 dry sheep equivalents per ha and weaners were treated with anthelmintics 3 to 6 times per year. Management procedures based mainly on anthelmintic therapy were effective in controlling nematode populations in weaner sheep, although many producers alternated between different groups of anthelmintics within the same year contrary to current recommendations for long-term preservation of anthelmintic efficacy. It was concluded that anthelmintic resistance was not of practical importance to the majority of sheep producers in the region.

Globoid cell leucodystrophy in polled Dorset sheep.

Globoid cell leucodystrophy (Krabbe's disease) was diagnosed in two Polled Dorset sheep from a stud farm. Clinical signs were hind limb incoordination progressing to tetraplegia. Histologic changes in white matter of the brain were myelin destruction, loss of oligodendroglia, astrogliosis and accumulation of distinctive periodic acid-Schiff (PAS)-positive globoid cells. The activities of galactocerebroside beta-galactosidase, the lysosmal enzyme specifically deficient in globoid leucodystrophy, and of three other glycosidase enzymes were compared in brain tissue of one affected and six unaffected sheep. Activities of the three nonspecific glycosidases were similar in all seven brains. Galactocerebrosidase activity was similar in the six control sheep, but in the affected brain was less than 6% of the control mean.

Tracheitis in sheep after oral administration of a mineral supplement.

Outbreaks of illness and deaths in sheep after the concurrent administration of a cobalt, copper and zinc mineral supplement and laevamisole are described. Clinical illness was characterised by profound dyspnoea and inability to exercise. The consistent postmortem finding was severe, necrotising tracheitis with partial occlusion of the airway. This lesion was reproduced experimentally by intratracheal administration of the mineral supplement dissolved in one particular formulation of laevamisole but not in water or another preparation of laevamisole. Further experiments revealed that combined zinc sulphate and copper sulphate dissolved in the particular formulation of laevamisole would produce the tracheal lesions.

Border disease: persistant infection with the virus.

Two genetically related sheep that produced border disease-affected lambs from successive pregnancies were identified. These sheep, and some of their progeny, were found to be persistently infected with a virus antigenically related to bovine virus diarrhoea/mucosal disease virus. Only one of the sheep developed detectable serum antibody to the virus, and this animal only produced it 12 months after being detected as infected. The epidemiological significance of sheep persistently infected with border disease virus is discussed.