The prevalence of lice (Bovicola ovis) infested sheep flocks in Western Australia (1987–1993)

SUMMARY The proportion of wool bale brands with a positive test for sheep lice in baled wool decreased from 29.5% in 1987/88 to 23.2% in 1990/91 before increasing to 38.2% in 1992/93. Changes in the proportion of wool bale brands with a positive test for lice were highly correlated with changes in the Wool Market Price Indicator. The increase in the proportion of positive lice tests since 1990/91 was associated with an increase in failures to eradicate lice from flocks. These failures were partly a consequence of the reduced use of lousicidal treatments, the development of resistance to synthetic pyrethroid chemicals and an increase in the transmission of lice between flocks.     

Presynaptic stimulation of dopaminergic CNS structures in sheep as a mechanism of immobilising action of Immobyl (fentanyl + azaperone)

The immobilising action of Immobyl (fentanyl : azaperone, 5:1) in six sheep has been analysed on the basis of the changes in dopamine, noradrenalin, adrenalin, homovanillic acid and 5-hydroxytryptamine concentrations in the corpus striatum, frontal motor cortex, pons, cerebellum and lumbosacral spinal cord as compared to the control animals which were given saline. Forty minutes after intramuscular injection of an immobilising dose (0.19 mg [kg bodyweight]-1), Immobyl caused a significant decrease in dopamine, noradrenalin and 5-hydroxytryptamine concentrations and a similarly large decrease in homovanillic acid concentration (47 per cent) in the corpus striatum with a simultaneous but insignificant increase in the concentrations of these substances in the frontal motor cortex region. In Immobyl immobilisation, sheep showed a significant increase in dopamine concentration with an equally significant decrease in homovanillic acid concentrations in the lumbosacral part of the spinal cord. It is suggested that fentanyl stimulates the presynaptic dopamine receptors in the corpus striatum in sheep, significantly decreasing synthesis and release of dopamine and noradrenalin and intensifying an inhibitory effect of the corpus striatum on locomotor activity and thus causes the immobilisation of the animal.     

Efficacy against sheep lice (Bovicola ovis) and fleece wetting of six shower dip preparations

Summary The relative efficacy of 6 shower dip chemicals most frequently used for the treatment of sheep lice (Bovicola ovis) in Western Australia was examined. Groups of 20 sheep infested with lice were treated with products containing either alphamethrin, cyhalothrin, diazinon or diazinon plus piperonyl butoxide and rotenone, formulated as emulsifiable concentrates, and with products containing either coumaphos or magnesium fluorosilicate, formulated as wettable powders. All treatments were applied through a shower dip (Sunbeam model SSD). Inspections for lice were conducted until 9 months after dipping. No lice were found on sheep treated with the 4 emulsifiable concentrate products. In contrast, treatment with the wettable powders, which contained either coumaphos or magnesium fluorosilicate as the active ingredient, did not eradicate the lice infestations. The degree to which the fleece was wetted was assessed 20 minutes after dipping and showed that the wettable powder dips penetrated the fleece less than the emulsifiable concentrate dips. Less fluid was retained by wool staples in an in-vitro test when dip wash was made with the wettable powders. It was concluded that the degree of wetting attained at dipping was an important factor in achieving eradication of sheep lice.     

Persistence of the sheep body louse, Bovicola ovis, after treatment

SUMMARY Lice were found in samples of baled wool from 198 of 464 flocks treated to eliminate an Infestation in the period July 1988 to June 1990. In 287 flocks the Insecticide was applied as a backline treatment and in 177 flocks a shower dip was used. Of these flocks, 41.5% and 44.6%, respectively, were found to be infested at the following shearing. After adjusting for the accuracy of the test, It was estimated that infestation in 2 consecutive 12-month periods occurred in 52.6% of flocks with a real incidence rate of 27.4%. Using these estimates, it was calculated that in 34.7% of infested flocks treatment did not kill all lice. There were no differences in the proportion of consecutive infestations between flocks treated with any of the 3 chemicals applied as backline treatments. Among flocks treated In a shower dip, 68.4% using coumaphos, 37.8% using diazlnon and 41.5% using cyhalothrin had consecutive Infestations (P < 0.05). The detection of lice in 63.2% of flocks that were treated with magnesium fluosilicate was, in part, attributed to the application of this chemical by one operator.