The ‘efficacy’ of a drench refers to its capacity to kill worms. Different application methods (formulations) of the same active ingredient can have different impacts. In a trial conducted in New Zealand, moxidectin administered orally was found to kill a higher percentage of small intestinal worms (Cooperia species, had a higher efficacy) than either pour-on or injectable forms of the same treatment. These findings have been confirmed in similar studies in South America, the UK and Europe, and it appears that oral and injectable formulations provide higher and less variable blood levels of the active ingredient than do pour-on products. A worm species diagnosed as ‘resistant’ to a chemical used in one formulation may be ‘susceptible’ when that chemical is applied in a different form.