Second, be sure you know what concentration your pharmacy sells. We've had some pergolide that was 1mg/ml, meaning the horse gets 1 ml of liquid to get 1mg of the drug. We've also had some that was 0.25mg/ml (4 ml liquid = 1mg of drug) and now use 0.20mg/ml (5 ml of liquid = 1 mg of drug.) One advantage to the more dilute form is a lesser difference in dose if you don't measure to the exact hair.
Finally, *when* you test ACTH levels has an effect on results. ACTH naturally increases as winter approaches and is lower in summer, so season will affect your test results.. Some people compensate by giving a different dose of pergolide in the winter than in the summer. We haven't done that, but it is something to be aware of.