Efficacy of orally administered ivermectin on lungworm infection in free-ranging bighorn sheep

Published source details Easterly T.G., Jenkins K.J. & McCabe T.R. (1992) Efficacy of orally administered ivermectin on lungworm infection in free-ranging bighorn sheep. Wildlife Society Bulletin, 20, 34-39.
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This study is summarised as evidence for the following.

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Use drugs to treat parasites

A replicated, controlled, before-and-after study in 1987–1988 in a state park in South Dakota, USA (Easterly et al. 1992) found that following medical treatment, lungworm larvae levels in bighorn sheep Ovis canadensis faeces reduced over the following month, but not 3–7 months after treatment. In the month following treatment, average concentrations of lungworm larvae in faeces of bighorn sheep treated with one dose (50–250 larvae/g faeces) or two doses of ivermectin (50–300 larvae/g faeces) were lower than in untreated sheep (500–1,400 larvae/g faeces). However, by 3–7 months after treatments, average concentrations of lungworm larvae did not differ significantly between treated (600–1,300 larvae/g faeces) and untreated sheep (300-600 larvae/g faeces). One group of free-ranging female sheep received alfalfa treated with the anti-parasitic drug ivermectin in February 1987 and 1988 (four and six individuals, respectively) and another group received it in both February and March 1987 and January and February 1988 (seven and 14 sheep respectively). Five (1987) and nine (1988) sheep were untreated. Each treatment was administrated over two successive days at a rate of 2 ml ivermectin/sheep, and sheep were pre-baited with untreated alfalfa two weeks prior to each treatment. Parasite counts were made through analysing sheep faeces collected weekly from January to March and June to August in 1987-1988.

(Summarised by: Ricardo Rocha)