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

Abstract

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.

Flavonoids and Related Compounds in Parasitic Disease Control

“…Rotenone has been proposed as a treatment for the honeybee mite Varroa destructor [65], the Atlantic salmon Plathyhelminth Gyrodactylus salaris [66], cattle hypodermosis [67] and the sheep louse Bovicola ovis [68].…”

Further evidence that zinc sulphate compromises the efficacy of dipping treatments using diazinon to control sheep lice (Bovicola ovis)

“…Higgs et al 4 found that wettable powder products were less effective at eradicating lice than four emulsifiable concentrate products. The poorer efficacy was attributed to the poorer wetting achieved, both in vivo and in vitro, with the powder products.…”

“…On days 22 and 23 after shearing (day 0 of the trial), the 200 sheep were weighed, ear-tagged and lice counted by a standard method. 4 The sheep were stratified on louse count into five categories, further stratified within category on shorn body weight, divided into groups of 10 sheep and allocated randomly to 10 treatment groups.…”

“…Ten sheep from each group were randomly selected for measuring fleece wetness, beginning 20 min after treatment. The visibly wet part of the staple, and the staple length, were measured at each of 10 sites (neck, shoulder, withers, flank and rump) as described by Higgs et al 4 Each group was held separately in pasture plots secured by electric outriggers on both sides of common fences. Ten sheep from each group were examined for lice at 1, 2, 3, 5 and 7 months after treatment using the 40 partings per sheep method of Higgs et al 4 All sheep were examined before termination of the trial at 9 months after shearing which was in December 1996.…”

“…Four weeks after shearing in March 1995, an estimate of the number of lice on each sheep was made using a standard method. 4 The sheep were stratified on lice counts into 15 strata and allocated randomly to three groups of 15 sheep which were treated in a Harrington U-shaped portable plunge dip 4 weeks after shearing. Two of the groups included zinc sulphate in the dipping fluid and the third was a control group.…”