COMPARISON OF THE REAPPEARANCE OF STRONGYLE EGGS IN FOALS, YEARLINGS,AND ADULT HORSES AFTER TREATMENT WITH IVERMECTIN OR PYRANTEL

The reappearance of strongyle eggs in faeces after treatment with iver mectin or pyrantel embonate was investigated in 22 foals, 36 yearlings , and 45 adult horses on five Dutch horse farms. The results confirmed earlier studies which showed an egg reappearance period of 9 and 6 we eks after ivermectin and pyrantel treatment, respectively, There were no differences between the egg reappearance periods of foals, yearling s, and adult horses. The mean egg counts of the yearlings were, howeve r, consistently higher than the mean egg counts of the adult horses an d foals in both ivermectin- and pyrantel-treated animals, It is conclu ded that shorter treatment intervals in foals and yearlings are not ob ligatory. However, longer intervals must be prevented in yearlings bec ause their contribution to pasture contamination is relatively high.