Control of lice on sheep with long wool.

Abstract

334 Proc. Aust. Soc. Anim. Prod. Vol. 17 CONTROL OF LICE ON SHEEP WITH LONG WOOL N.S. SHERWOOD* and S.W. PAGE* SUMMARY The lousicidal activity of three synthetic pyrethroids as a dip wash was evaluated. The minimum effective concentration of alphamethrin was found to be less than 2 mg/L while for cyhalothrin and cypezmethrin it exceeded 4mg/L. All treatments,as jetting fluids at 5Omg/L,failed to remove lice. A low volume 5Og/L alphamethrin backline treatment eradicated lice in sheep with 6 months wool. control. Keywords : Damalinia ovis, pyrethroids, dipping, jetting, backline, lice INTRODUCTION The body louse of sheep, Damalinia ovis,is widespread throughout Australia with a Western Australian survey (Wilkinson et al 1985) indicating lice in 26% of flocks in the Kojunup shire and a south western Queensland study showirg lice present on 29% of properties (Dunlop 1982). Lice cause host irritation leading to -1 derangement. Econrmnic losses are due to both decreased -1 production and the costs of lice control. Less greasy and clean tl is produced (Wilkinson et al 1982; Niven and Pritchard 1985; Eliott et al 1986), with a higher percentage of fleeces dwaded due to totting and increased yellowness (Kettle and Lukies 1982). Evaluation of the value of lost wool production and the costs of treatment and statutory control yielded an estimated loss to the national trl~ol industry of $94m (Wise 1987). Studies conducted to explore the possibility of lice eradication in W.A. (Wilkinson 1977, 1980, 1986; Wilkinson et a1.1982, 1985) indicated t&t the main deficiencies in the control programmes were the failure to detect lice in infected flocks a& to eradicate the disease when identified. The main sources of new infestations were purchased sheep arrd strays. In recently shorn sheep, lice infectians may be difficult to detect. Allied to this it was thought the practice of routine off-shears treatment disguises infestation in so= flocks. It w proposed that to achieve eradication prophylactic treatment should not be recked arx3 intervention to control lice should only be attempted after positive diagnosis. While adoption of the Lice Detection Service offered by the AWTA improves detection (Wise 1987) a major drawback remains- the lack of suitable treatments for controlling lice in long wool. This paper examines the efficacy of various synthetic pyrethroids applied to sheep in long wool by either of three techniques : dipping, -jetting & lowvolumebacklineapplication. Dipping and jetting studies were conducted with emulsifiable concentrate formulations of 47.5g/L cypesnaethrin (Robust; Robert Young Pty Ltd), 5Og/L cyhalothrin (Grenade, ICI Australia Ltd) and lOOg/L alphamethrin (SmithKline AninralHealthProducts). Backline stud&&were conductedwithanaquleaus suspension of 5&3/L alphamethrin (Vanquish, SmithKline Animal Health Products). * Smith, Kline and French Laboratories (Australia) Pty. Ltd., Brookvale, N.S.W. 2100. Proc. Aust. Soc. Anim. Prod. Vol. 17 Sheep to be dipped were immersed in an appropriately charged 600 litre stainless steel plunge dip for 1 minute. 335 Hand jetting B carried out using a Finsbury puq delivering fresh fluid through a five nozzle Rega handpiece, v&ich delivered wash at a rate of one litre per ten seconds and a pressure of 500 KPa. Thehandpiece~ canbed slawlythrough the-1 frunthenapeof thenecktothe rumpinthree parallel Bps. Twentysecondswas spenttreatingeachsheepinexperiment2 mile sheep in experiment 4 Wre treated to saturation. The lc~ volume backline treatment was applied frun a backpack with a Vanquish spray-on applicator delivering a 12cm band frun the base of the neck to the rump on the dorsal surface of the sheep. All sheep were weighed before ZtIEd after treatment using electronic scales. Six mks after shearing, 50 four tooth merino others wzre lice counted, and randanly divided into groups of five sheep for treatment with water or 1, 2 and 4 mg/L of cypermethrin, cyhalothrin or al@amethrin. Groups were reevaluated at 1,2,4,10 and 15 meks after treatment. mriment 2 Lice control by jetting Fifteen, mean mid side three groups alphamethrin, conducted at four tooth merino wethers with a heavy lice infestation and wool length of 5.5cm were lice counted & rarrdomly divided of five, for treatment with either cypermethrin, cynalothrin each at a rate of SO&L. Post treatment lice assessments 1,2,4,6 a.rd 15 weeks. a into or were Brpermt 3 Lice control by backline treatment Fifteen four tooth lice infected merino wethers with six months -1 ere licecountedand randanlyallocatedtothreegroups. Group 1 remained untreatedwhilegroups 2 and 3 received 250nrgor 500mgrespectivelyofthe alwthrin law volume backline formulation. Reevaluations occurred 3,8,13,15,22 and 29 weeks after treatment. 336 Proc. Aust. Soc. Anim. Prod. Vol. 17 Bqzriment 4 Field comparison of backline arad jetting treatments A field trial MS undertaken at Goulburn on a mob of 442 mature Merino wethers, with a mean live wight of 48lq and carrying 10 months mol of staple length 8cm. The mob was divided randunly into four groups with lice evaluations made on10 sheep frun eachgroup. Group 1 (50 s-p) was left untreated, Group 2 (170 sheep) received 20mL of an al@mrrWhrin backline treatment, while the remaining twp Groups 3 and 4 wre hand jetted to saturation with either SOmg/L cyhalothrin (111 sheep), or SOmg/L alphmethrin (111 sheep). RESULTS AND DISCUSSION A summary of group sheep lice counts for experiments 1,2,3 and 4 is presented in tables 1, 2, 3 and 4. No signs of insecticidal toxicity were observed. Table 1 Mean lice counts following various low rate plunge dip treatments Table 2 Group mean lice counts follming various hand jetting insecticide treatments at SW/L. Table 3 Mean lice counts follmving backline treatment with alphamethrin formulation. Proc. Aust. Soc. Anim. Prod. Vol. 17 Table 4 Lice count following various treatments in 10 months -1. (Goulburn Trial) 337 If lice control is attempted by dipping a minimum dip wash concentration of approximately 1 - w/L alphamethrin muld remove lice. This study indicatedthattheminimumeffectivedose of cyi&lothrinand cypermethrin exceeded 4mg/L. At this rate the corrected percent lice reduction 15 weks after treatment was 99.6% and 98.7% with cyhalothrin or cypemthrin respectively. Hand jetting at 5Omg/L with all treatments failed to reme lice. While percent reduction over pre treatment lice levels (alphamethrin - 99.546, cypermethrin 93.6% ard cyhalothrin 82.3%) indicate good lice control, none of the treatments achieved eradication of lice. Both dose rates (25Ong and SOOJ~) of the alphamethrin backline formulation rem lice from sheep with six months wool The Goulburn field trial confirmed these results with eradication of lice being observed with the backline treatment, while U jetting with alphamethrin or cyhalothrin achieved reductions of 90% aM 82% respectively. The availability of low volume backline treatment such as the one examinedprovidesameans of eradicatiq lice in any wool length. A long -1 backline treatment does not require the marqower, plantandtimeassociated with jetting, and does not expose lice populations to sub lethal doses of insecticide. Lice infested pregnant m can be all- to complete lambing before trea-t, introduc& or purchased sheep can be -antined arrd treated, arvlwithmultiple smings, shornmobsmaybetreated conventionally off shearswhileunshormlnobsmaybetreatedwiththelo~woolbackline treatment. Elliot, 'J., Jones, A.L., and Pauley, J.A. (1986)Aust.Adv.Vet.Sci. p 125. Kettle, P.R., and Lukies, J.M. (1982)N.Z. Exp mic.10:15. Niven, D.R., and Pritchard, D.A. (1985)Aww27 Wilkinson, F.C. (1977). Proc.54th Ann.Conf.Aust.V&Ass. p 164. Wilkinson, F.C.(1986) Aust Adv Vet Sci. p 130. Wilkinson, F.C. (1980) Veterinary Epidemiology and Econunics. Proc.2nd.Inter.Symp.Canberra. p 396 Wilkinson, F.C. de Chaneet, G.C. and Beetson, D.R. (1982) Vet.Parasit.9:243 Wilkinson, F.C., Norris, R. and Roberts, J (1985)Aust.Adv.Vet.Sci. p 127. Wise, G., (1987). Proc.Wool,Productivity and Marl&&q Seminar,Vni of N.S.W.: Kensing-ton. Dunlop, L (1982) The Mulga Line, 2/86:6