Economic evaluation of three anthelmintic strategies for lamb flocks affected by benzimidazole-resistant nematodes.

Abstract

To compare the profitability of three anthelmintic strategies in growing lambs in flocks with nematodes resistant to benzimidazole anthelmintics. A partial-budgeting analysis was carried out by means of a stochastic simulation model, which allows inputs to be described as distributions rather than as fixed values, and hence permits variation between farms to be considered in the analysis. The results show that control of nematode parasites by use of an effective anthelmintic provides the highest net returns, yielding a margin over ineffectively treated lambs of A$114 per 100 lambs on average. Suppressive treatment based on the administration of two controlled-release capsules and monthly with moxidectin resulted in an average loss of A$131 per 100 lambs in comparison with animals treated with an ineffective anthelmintic. Analysis of the results from capsule-treated lambs did not take into account the unmeasured benefits associated with less contamination of pastures. Sensitivity analysis using a stochastic model indicates that apart from the effect of treatment on weight gain variation in carcase price greatly influences the profitability of all the parasite control programs examined. The results suggest that it is economically important for farmers to adjust their strategy in the presence of anthelmintic resistance. But as a result of uncertainty in the factors influencing economic return, the expected economic benefit is likely to vary substantially.