All horses require periodic treatment for parasites during a lifetime. In order to minimize the infection with parasites, you should regularly remove the droppings from the horse’s field, shed or stall, periodically move your horse from one field to an empty one, or populate it with species that do not hold the same parasites as equines, for example ruminants. Even with these measures, there is a small chance of infection with internal parasites, thus modern horse owners give periodically anthelmintic drugs, a wormers medication type, which removes the internal parasite population from your horse.
Two methods prevent your horse from infection with intestinal worms. These are purge dewormers, which act in a single dose and kill the internal parasites or continuous dewormers, which are mixed in daily with the food of the horse. The two methods act differently, thus with different results. The purge dewormers are a stronger mix, which kills all the parasites in the body, but it lasts only a few weeks in the body of your animal, thus it has to be repeated frequently. The continuous dewormers are a milder dose which is easier on the body of the horse, but it might become ineffective after a while, because it can lead to drug resistance.
A more scientific way of treating your horse against parasites is to perform fecal egg counts on manure and deworm only the infected horses. In this manner, you will reduce the probability of drug resistance. Even if the results are negative almost all the time, veterinarians still recommend deworming your animal at least once or twice a year. This treatment comes in various shapes, including gels, powders, granules, pellets and pastes. Granules and powders are a usual shape for the purge dewormers, while gels and pastes come in plastic syringes which must be inserted into the horse’s mouth, under its tongue.