A Field Survey on Resistance of Gasterointestinal Nematodes to Levamisole in Sheep in Khuzestan Province of Iran

To determine resistance of sheep nematodes to levamisole. Design: Exprimental field survey. Animals:In this survey, 15 sheep flocks were selected from three geographical regions of Khuzestan province including mountainous, hilly and plain area. On each flock, 30 sheep were randomly distributed into two groups (control and test) of 15 animals each. Procedure: Faecal egg count reduction test was performed according to guidelines of W.A.A.V.P.1 and precentage of faecal egg count reduction was calculated for each flock. In the resistant flocks, faecal culture and necropsy of untreated and treated groups, were used to determine resistant species of the nematods. Statistical analysis: Drug resistance was detected if: i) the precentage of reduction in egg counts was less than 95% and ii) the 95% confidence level was less than 90%. ANOVA and t - test were used for analysis of the results.

Results of faecal egg count reduction test showed that 66.6% of the flocks were resistant ones, 13.4% suspected to be resistance and the rest susceptable to levamisole.

This survey showed that levamisole efficacy in the sheep flocks of highland regions in Khuzestan province reduced significantly.This reduction is due to development of resistant isolates of Ostertagia circumcincta and Tricbostrongylus vitrinus in the resistant flock.