Horse Health - Worming Horses

One of the hardest programs to manage when I ran a large private horse stables was to get all the boarders and their horses on a routine worming program. Despite the rules, despite automatically adding the cost of wormer to their board bill, owners had a hard time abiding this important and routine agenda of horse health. Some of that was surely their inability to give a horse wormer which they ain't necessarily fond of to begin with.

Anthelmintics, or horse wormer needs to administered to each horse not only on a routine basis but on a program designed to be effective against the parasites and minimize the chance of the parasites being resistant to the worming product. It is not simply a matter of picking up a tube of wormer at the feed store several times of year. Worming products need to be rotated to ensure effectiveness against various parasites.

The various worms that we use a worming program to combat include:
Tapeworms. Tapeworms can contribute heavily to colic. A horse affected with Tapeworms may appear to be poor (malnourished) as they affect the horse’s digestion process. I have seen a horse heavily infected with Tapeworms colic bad after being wormer for the first.

Bots. The adult Bot looks like a potatoe bug and lay their eggs on the hair of the horse. As the horse licks itself they ingest these Bot eggs which eventually travel to the stomach and can cause damage to the horse.

Large Strongyles. Found in the large intestine, adult Strongyles burrow themselves into the large intestine walls. Strongyle eggs are passed in the manure where they hatch and are ingested by the horse completing this cycle. Strongyles can damage the blood vessels and cause colic and blood clots.

Pinworms. Picked up by horses through feed, water and from the ground, Pinworm eggs can cause a horse to rub his tail against a fence or pole and at worse damage the tail or at least rub hair off.

Roundworms: Picked up by horses grazing, these worms are found in the intestines. As adults, roundworms are normally found in the in the small intestines and sometimes passed in the manure. Traveling through the blood supply, the eggs of Roundworms will travel to the lungs and the liver affecting the health of the horse.

Worming schedules. There are many different worming schedules based on the area you live in and whether your horses are turned out with others and on pasture. The most common worming schedule is a bi-monthly schedule, giving a different wormer every other month. Most Horse Supply Product catalogs with feature several different such schedules. One schedule may be:

Jan/Feb – Pyrantel/Praziquantel (for Large/Small Strongyles, Roundworms and Pinworms – Praziquantel additionally for tapeworms)
Mar/Apr – Fenbendazole (for Large/Small Strongyles, Ascarids and Pinworms)
May/Jun – Ivermectin (for Large/Small Strongyles, Ascarids, Bots and Pinworms)
Jul/Aug – Pyrantel/Praziquantel (for Large/Small Strongyles, Roundworms and Pinworms – Praziquantel additionally for tapeworms )
Sep/Oct – Fenbendazole (for Large/Small Strongyles, Ascarids and Pinworms)
Nov/Dec - Ivermectin (for Large/Small Strongyles, Ascarids, Bots and Pinworms)

With the introduction years back of combination worming products, I have opted for a quarterly worming schedule. When I bring a new horse in, I quarantine him for three weeks and catch him up on the worming program as well as vaccinations and a Coggins (EIA) test.

Feb Fenbendazole
(Safeguard or Panacur, I’ll rotate from year to year which brand)

May Praziquantel with Moxidectin
(QuestPlus)

Aug Ivermectin
(Zimectrin)


Nov Ivermectin with Praziquantel
(Zimectrin Gold)

Be careful to administer the correct amount of wormer to your horse. Use the scale on the stem of the worming syringe to set for that horse’s weight. It is always a good idea to get a fecal egg count for parasites by your vet before administering wormers for the first time to a new horse. I said before, a horse being wormed for the first time may drop a bunch of parasites which can cause a blockade and colic that horse. Talk to your Vet before giving wormers to a Broodmare in foal and to standing foals.

I do not use daily pellet wormer. I know good horse people that do, but it seems to me like it’s a lot easier for the parasites to build up a resistance to daily, therefore a lesser strength product. Again, talk to your Vet, present him/her with a worming schedule and ask their opinion for that area and environment before beginning your worming program.