The Goal of a Good Horse Worming Schedule

The goal of any parasite control program is to minimize the risk of parasitic disease, control parasite egg shedding and maintain the effectiveness of drugs. Traditional parasite control programs involving the rotation of various anthelmintics at regular intervals have created parasite resistance to horse wormers. Anthelmintics are medicines which expel parasitic worms especially of the intestine. As a result of medication resistance, it is important that your current horse worming schedule prevent this and in turn maintain the effectiveness of drugs for future generations of horse owners.

Fecal Egg Count

To accomplish the goals of your parasite control program, a fecal egg count (FEC) should be performed to determine the amount of egg shedding of an individual horse. A FEC is simple to complete, however, it requires the use of a microscope. Limitations of equipment requires FEC to commonly be performed at your veterinarian’s office. When collecting a fecal sample, it should be fresh, stored in an airtight/leak-proof container or plastic bag, and refrigerated. Samples should be tested within seven days of collection. In interpreting the results of a FEC, 1-200 eggs per gram (EPG) is considered a low shedder, 200- 500 EPG is a moderate shedder, and >500 EPG is a high shedder. Most horses will have a parasite load, since they are part of nature. The key is to minimize and prevent clinical signs by maintaining equilibrium in the animal.

Things to Consider

When designing your horse worming schedule, environmental influences and management practices should be considered. These factors will have a significant impact on the parasite loads of equine managed at a facility. Adequate grazing is important to maintain pastures which are not too tall or too short. A pasture that is less than three inches tall will result in your horse ingesting all larval and egg stages present. However, horses with limited access to pasture or on dry lots with the absence of grass often have lower FECs. The number of horses sharing a pasture should be considered, as overstocking results in a high level of parasite exposure. Horses that are pasture mates will commonly share the same population of parasites and resistance. Animal interaction, such as exposure to wildlife, new horses or visitors should also be considered. New horses should be quarantined, especially if history of deworming, vaccinations and coggins is unknown. Visitors can also include human visitors who have horses of their own. This can result in the tracking of feces on their boots. In addition, equipment can transport unwanted parasites, reiterating the importance of manure management and fly control.

Different Types of Horse Wormer

Various treatment options are available. Fenbendazole (Safe-Guard, Panacur) interferes with the worm’s energy metabolism on a cellular level. Pyrantel pamoate (Strongid) acts at the neuromuscular junction causing irreversible rigid paralysis. Praziquantel (Zimecterin Gold, Equimax, Quest) is the only horse wormer that is effective against tapeworms. In the United States, praziquantel is only available in combination with ivermectin or moxidectin.

How Often Should You Worm Your Horse?

Your parasite control program goals can be achieved with one to two treatments of wormer each year in most cases. Treatments should be focused on seasons of peak transmission (fall and spring). A spring deworming with a fenbendazole or pyrantel pamoate and a fall treatment of ivermectin with praziquantel is sufficient in most horses. All additional treatments should target horses with high FEC and those which display clinical signs of parasite infestation. Dosage required for your horse is determined by weight. It is important not to under-dose. When scales are not available, a weight tape or equation can be used to determine a horse’s body weight. Always be cautious and consult your veterinarian when putting together your horse worming schedule.