How to Administer Deworming Medicine in Horses

At one time, most deworming was done with a stomach tube by a veterinarian, because many older products were caustic to the horse’s gastrointestinal tract. Today, most horses are given an oral dewormer as a paste or gel by the horse owner or farm manager. Research has shown that paste or gel deworming is as effective as tube deworming. Oral deworming is also more convenient and far safer than tube deworming.


The following procedure prevents horses from spitting out an oral dewormer:

First – Rinse out the horse’s mouth with several 2-ounce syringes of water, directing a stream of water between teeth and cheeks. This loosens grain or hay to which dewormer could stick and prompts the horse to spit it out.

Second – Place your left thumb in the back of the horse’s lips in the space between the incisors (front teeth) and the premolars (cheek teeth) where there are no teeth.

Third – Insert the end of the tube alongside your thumb so the paste or gel will be placed on the horse’s tongue at the back of its mouth. Gently squirt the dewormer onto the horse’s tongue. Next, raise the horse’s head and/or massage its throat latch to encourage swallowing.

Frequency of Deworming

Frequency of use of any dewormer depends on how long it takes between treatment and the reappearance of large numbers of parasite eggs in the animal?s manure. This interval is known as the eggs? re-appearance period. It is necessary to use a dewormer every 30 days if parasite eggs re-appear within this time period.

In the past, most dewormers were used every 30 days. That procedure changed with the discovery of ivermectin and moxidectin, which keep parasite numbers down longer than other dewormers currently on the market. Ivermectin consistently depresses parasite egg numbers for about 60 days, while moxidectin is effective for about 90 days. Deworming less frequently with ivermectin or moxidectin also helps prevent parasite resistance and puts less stress on horses.

Horses can also be dewormed daily. Daily feeding of pyrantel tartrate (Strongid-C or Strongid-C 2X) prevents infection with small and large strongyles, roundworms, and pinworms that the horse can pick up while grazing. Pyrantel tartrate is not effective against bots, however.

Daily deworming prevents parasite infections, halts migration of some parasites, and reduces the tissue damage parasites cause. Manure from continually dewormed horses can be spread on horse pastures, because it contains no living stages of strongyles.

There are some disadvantages to such a program. Cost may be more than periodic purge doses, horses raised on continual dewormers may not develop natural resistance to parasites such as roundworms, and horses removed from continual deworming may exhibit severe clinical signs of parasite infection when finally exposed to internal parasites.

Parasite Control without Deworming

Deworming is the most common method of controlling internal parasites in horses. However, it is not the only method. Research has shown that removing manure piles from a horse’s pasture two or three times a week is more effective than using dewormers to control internal parasites. One study noted that dewormed ponies had five to 10 times the parasite load of ponies not dewormed but kept in pastures where the manure was removed.

Obviously, keeping horses in pastures where manure has been removed is not a practical consideration on large pastures because expensive equipment would be required. On small pastures, this method has merit. It would also increase grazing forage, since horses normally do not graze the rough (tall forage) areas where they defecate. Owners who keep horses in a suburban or urban area may want to use this procedure to provide more pasture forage for grazing and a more aesthetic environment, which would also aid in controlling flies attracted to the manure.

From eXtension HorseQuest.