I have a 12-year-old gelding on a regular deworming program (I rotate ivermectin, pyrantel pamoate, fenbendazole, and praziquantel/ivermectin) and he’s very healthy. Is there any problem with exercising him on the same day that I deworm? Should he get some time off after deworming?

For a horse that has been on a regular, well-balanced deworming program, there is no reason why you cannot exercise him on the day the dewormer is administered. The word “regular” conveys a meaning of at least several times a year. Depending on stocking rates (horses per acre) and management, most horses benefit from deworming at least every three months. The chemicals that you have listed are excellent choices and should be quite effective in reducing parasites in your horse.

If your horse had not been dewormed in a long time, particularly if he were quite young, there would be a slight risk of colic after deworming due to a heavy parasite load being expelled. In that scenario, it might be advisable to give the horse that day off after deworming, or consider a half dose of a fenbendazole product, to avoid killing large numbers of ascarid parasites at once. This half dose would then ideally be followed up within several days with an ivermectin or moxidectin dewormer.

Julia H. Wilson, DVM, Diplomate, ACVIM, associate professor & division head, Large Animal Medicine, Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota.