| sheep-farm risk factors for ivermectin resistance in ostertagia circumcincta in western australia. | on-farm risk factors associated with ivermectin resistance on sheep farms in western australia were identified from data derived from a postal survey of 235 farmers who had conducted a fecal egg-count-reduction test in 1999, 2000, or both years. a response of 54% was achieved. we developed a logistic-regression model. contributory main effects in the final model were selling 10% more sheep in 2000 than is the usual policy (or = 4.00), farm purchased since 1975 (or = 2.34), and number of winter f ... | 2004 | 15158574 |