When designing a parasite control program, you should consider many factors, such as horse age, housing and feeding management, horse use, and parasite resistance patterns on the farm. Some examples of management systems that may not be effective for continuous dewormers include group-fed animals or those that are not fed grain on a consistent basis. Also, if there are multiple people with varying levels of experience doing the feeding, there might be a concern about consistency in both dosage amounts and actual feeding of the dewormer.
Also, to determine if a particular paste dewormer is effective on a particular farm, a fecal sample should be taken from the horse(s) before deworming and then about 10 days later to see if the drug was effective. To determine if a continual dewormer (pyrantel) is effective, fecal samples can be evaluated after the horse has been on the drug for a few weeks.
Horses that receive a continual dewormer will need to be paste dewormed at least twice a year since pyrantel is not particularly effective against certain parasites or certain stages of a parasite's life cycle. Parasites that are migrating through the body's tissues, bots, and tapeworms are not controlled with feeding a continuous dewormer (pyrantel).
