Mode of action of back-line application of spinosad, a non-systemic parasiticide, on sheep
L. B. Lowe A D , K. C. Hacket A , J. T. Rothwell B and P. Nicholls CA Elanco Animal Health, Level 5, 123 Epping Rd, Macquarie Park, NSW 2113, Australia.
B Faculty of Veterinary Science, University of Queensland, St Lucia, Qld 4067, Australia.
C PO Box 10, Menangle, NSW 2568, Australia.
D Corresponding author. Email lowe_l_barry@lilly.com
Australian Journal of Experimental Agriculture 46(7) 857-861 https://doi.org/10.1071/EA05333
Submitted: 23 November 2005 Accepted: 13 March 2006 Published: 8 June 2006
Abstract
Spinosad, applied as a jetting solution or dip is an efficacious, non-systemic treatment for the control of Bovicola ovis in sheep. This paper describes the effect of back-line treatment width and group housing of animals on the efficacy of spinosad for the control of lice. A 0.4 mg/kg liveweight dose was found to be the suboptimal dose of spinosad for the control of body lice in a dose titration study and was used to investigate application and housing effects in a second study. Lousy Merino sheep were treated with either a narrow 3-cm application of spinosad or with a wider 25-cm swathe. After treatment they were either kept alone or in groups of 6 sheep per pen. Lice were counted at day 0 and every 14 days to 70 days after treatment before estimation of the percentage of lice control and analysis of treatment effects. A much higher percentage of lice control was achieved with 0.4 mg/kg in the second study than in the first, possibly because of differences in formulation used. The wider application width gave significantly higher (P<0.05) control of lice than the narrow application when sheep were either housed alone or in groups up to day 42 post-treatment. Greater control of lice was seen in group-housed sheep compared with sheep housed individually (P<0.05) up to day 70. Using broader application widths combined with holding the animals together after treatment with pour-on formulations may optimise the delivery and efficacy of ectoparasiticides for livestock.
Additional keywords: application method, back-line, Bovicola ovis, ectoparasiticides, housing, pour-on, sheep lice, spinosad.
Acknowledgments
The authors wish to thank Kim Dawson for skill and professionalism in experimental animal management and Allan Darwish for preparation of the wool grease fraction.
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