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Effects of reproduction, genotype and anthelmintic treatment of ewes on Ostertagia spp. populations

Donald, A.D., Morley, F.H.W., Waller, P.J., Axelsen, A., Dobson, R.J. and Donnelly, J.R. (1982) Effects of reproduction, genotype and anthelmintic treatment of ewes on Ostertagia spp. populations. International Journal for Parasitology, 12 (5). pp. 403-411.

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Merino and Border Leicester × Merino (BL × M) ewes, nearly all of the same age and reared at the same site, were either unmated or mated to Border Leicester rams. Ewes of each genotype and reproductive status were untreated or were given a single pre-lambing drench with thiabendazole at 50 or 100 mg/kg a week before the start of lambing in spring on pastures at Canberra which had been contaminated during autumn and winter by adult sheep. The two genotypes grazed together within each combination of reproductive status and anthelmintic treatment which grazed separately. Thiabendazole was highly effective in removing both fourth stage larvae and adults of Ostertagia spp., the most abundant genus. Eight weeks after the pre-lambing drench lactating ewes carried larger Ostertagia spp. populations than did unmated ewes of both genotypes, but as a result of reinfection after treatment, differences between drenched and undrenched ewes were not significant. At this time lactating as well as unmated ewes harboured large populations of arrested early fourth stage larvae of Ostertagia spp. acquired during the last 8 weeks, showing that arrest of development is not prevented by lactation. There was strong evidence that some ingested larvae which became arrested in lactating ewes were rejected by unmated ewes. At all stages of the reproductive cycle studied, BL × M ewes were substantially more resistant to Ostertagia spp. infection than Merinos. No persistent benefits in parasite control or in animal production were detected from the pre-lambing drench.

Item Type: Journal Article
Publisher: Elsevier BV
Copyright: © 1982 Published by Elsevier Ltd.
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