Anticoccidial activity of arprinocid and halofuginone

Halofuginone and arprinocid, new anticoccidial drugs, were tested to determine the time of peak activity in the life cycle of Eimeria and whether they were coccidiocidal or coccidiostatic. Halofuginone was completely effective if medication was initiated by Day 3 postinoculation, but only partly effective if given on Days 4–7. Arprinocid was effective if given on Days 2–7 postinoculation, but only partly effective if given on Days 3–7. When medication was started on Day 0 and withdrawn on various subsequent days, good activity was recorded with halofuginone if the drug was given up to Day 1 postinoculation, but arprinocid required feeding up to Day 4 postinoculation. In other studies, medication was given until Days 6 or 7 postinoculation, then discontinued, to allow further development of coccidia that were arrested by the drug. With halofuginone, the oocyst passage was low with E. tenella and E. maxima, but moderate with E. mivati. With arprinocid, oocyst passage was low with E. maxima and E. mivati but moderate with E. tenella. These results suggest that halofuginone is active over a broader part of the life cycle than arprinocid, but both drugs had a predominantly coccidiocidal action.