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Implementing A Horse Worming Schedule

From Alpha Horse

It is surprising how many horsemen do not incorporate any form of horse worming schedule in their routine, seemingly just choosing a box of horse wormer at random and thinking that will do the trick. While it is true that there are many fine horse worming products available to horse owners, ultimately if you wish to keep your equine friend as protected against the multitude of parasites just dying to infest your horse you will need to draw out an effective plan of action.

Yes, this means you must incorporate the various forms of horse wormers into an organized horse worming schedule that targets the various parasite groups during the times of year they are most a threat.

As a quick side note, technically the terms we should use are de-worming and de-wormers, but since most horsemen remove the "de" when discussing this topic we will do the same.

Before jumping straight into the actual recommended horse worming schedule I would like to put out this caution: if your horse is already seriously infested with parasites you should be very careful about giving him a dose of paste wormer. A paste horse wormer could conceivably kill too many parasites at once, thereby causing them to bunch up in the horse's veins, intestines and colon. While this can kill a horse, more often then not it will just cause significant discomfort… but do we really want to cause discomfort to our equine friends?

In such cases I would start the worming process with a pellet wormer such as Strongid C2X. Since pellet-based wormers are mixed with a horse's feed daily, the potency is far lower than actual pastes. This lower potency allows for a slower and healthier parasite kill and removal rate. I advise putting a parasite-infested horse on a pellet-based wormer for at least one week before advancing to the standard paste regimen.

You must be careful to apply the recommended dose of horse wormer with each session, because parasites possess the ability to build a resistance towards agents designed to kill them when the agents are not applied in doses strong enough to kill the parasites outright. This is why it is also important to rotate the various types of horse wormers – not only does it increase the spectrum of targeted parasites, it makes it difficult for parasites to build up any sort of resistance or immunity.

Following is a solid horse worming schedule that we recommend:

Horse Worming Schedule
Month One A fenbendazole-based product such as Safe Guard.
Month Three An ivermectin-based product such as Zimecterin Gold.
Month Five A pyrantel pamoate-based product such as Strongid.
Month Seven An oxibendazole-based product such as Anthelcide EQ.
Month Nine A moxidectin-based product such as Quest.
Repeat Rotation

Please note that Moxidectin is NOT recommended for foals or weak horses since an overdose can be very dangerous to them.

The above horse worming schedule will suit most standard horse needs very well, but if your horse is one that grazes frequently you may want to modify it a bit to include a five-day double-dose schedule of a Fenbendazole-based wormer in October and February. This purges your horse's system of encysted larvae that are picked up easily during regular grazing. Since encysted larvae are very difficult to nail without the use of Moxidectin, the five-day regimen is necessary; you won't be able to purge a horse's system of this parasite with just one or two doses.

Note: Under no circumstance should you provide a double dose of Moxidectin. Although effective against larvae and bots with just one dose, multiple doses can be a danger to your horse.


Sample Paste Wormer Rotation Schedule
6 times per year, every other month recommended worming

from Horse Health USA

adapted from John Lyons

Anthelcide EQ Paste  or oxibendazole
Panacur Paste  or fenbendazole
Safe-Guard Paste fenbendazole
ComboCare  or 2% moxidectin & 12.5% praziquantel
Equell Paste  or 1.87% ivermectin
EquiMax Paste  or 1.87% ivermectin &
14.03% praziquantel
Equimectrin Paste  or 1.87% ivermectin
Horse Health Ivermectin Paste  or 1.87% ivermectin
IverCare Paste  or 1.87% ivermectin
Quest Gel  or moxidectin
Rotectin 1.87% Paste  or 1.87% ivermectin
Zimecterin Paste  or 1.87% ivermectin
Zimecterin Gold Paste 1.55% ivermectin &
7.75% praziquantel
Equi-Cide Paste  or pyrantel pamoate
Rotectin P Paste  or pyrantel pamoate
Strongid Paste  or pyrantel pamoate
Strongylecare Paste  or pyrantel pamoate
TapeCare Plus Paste pyrantel pamoate
Anthelcide EQ Paste  or oxibendazole
Panacur Paste  or fenbendazole
Safe-Guard Paste fenbendazole
ComboCare  or 2% moxidectin & 12.5% praziquantel
Equell Paste  or 1.87% ivermectin
EquiMax Paste  or 1.87% ivermectin &
14.03% praziquantel
Equimectrin Paste  or 1.87% ivermectin
Horse Health Ivermectin Paste  or 1.87% ivermectin
IverCare Paste  or 1.87% ivermectin
Quest Gel  or moxidectin
Rotectin 1.87% Paste  or 1.87% ivermectin
Zimecterin Paste  or 1.87% ivermectin
Zimecterin Gold Paste 1.55% ivermectin &
7.75% praziquantel
Equi-Cide Paste  or pyrantel pamoate
Rotectin P Paste  or pyrantel pamoate
Strongid Paste  or pyrantel pamoate
Strongylecare Paste  or pyrantel pamoate
TapeCare Plus Paste pyrantel pamoate

Dewormers with different active ingredients are effective against different types of worms.  To keep your horse in tip-top shape, it is important to rotate dewormers to prevent dewormer resistance from developing.

This schedule is a very basic dewormer rotation program. If you suspect your horses may have tapeworms or would like a deworming program customized to your region or conditions, consult your veterinarian for a course of treatment.

If you feed a daily dewormer be aware that it is not effective against bots, so you should deworm once in the fall and once in the spring using a 1.87% equine ivermectin paste dewormer to control bot infestations.

Deworming Tips

  • Use Ivermectin as your base deworming drug.
  • Read what each dewormer is "effective against." Many new dewormers are
    also now "effective against" tapeworms.
  • Choose the brand you like the best or best value/price (according to what it is "effective against" and your needs).
  • Be sure to get an accurate weight measurement for correct dosages.
  • Be sure to clean up any spilled dewormers, since it can be toxic to other animals.

Show Horse, Mare & Foal Schedule 

from Equine Research

Since many of our horses are show horses we do have a schedule for routine check-ups and vaccinations that must be followed:
Adult Horses
Coggins test
Double dose of pyrantel
Vaccinate for flu/rhino sleeping sickness, tetnus,potomac fever, rabies, Check teeth
worm with panacur
worm with wormer of your choice
Worm with Ivermectin, vaccinate for flu/rhino
Worm with panacur


8 weeks
must contain Eastern and Western Encephalitis

first dose
9 weeks
must contain Eastern and Western Encephalitis

second dose
12 weeks
Tetnus and Strangles
First doses for both
13 weeks
Second Dose
14 weeks
Third dose
16 weeks
First Dose
Second Dose
20 weeks
Second Doses for both
24 weeks
Venezuelan Encephalamylitis
first and only dose
The adult schedule will be used


While the broodmare does need special attention the injection and worming schedule is pretty much the same with a few exceptions
same as adult schedule and also one month prior to foaling
First dose is prior to breeding
at 5 months pneumobort (killed virus), at 7 months and at nine months
same as adult schedule but also one month prior to giving birth and also one month after foaling
Rabies can be given during pregnancy
****Do not give strangles injections during pregnancy****
written by Equine Research



Deworming Your Horse

Here's a simple, two-step plan to help you design a top-notch deworming program that is best suited for your horse.

By Karen E.N. Hayes, DVM, MS


When it comes to deworming your horse, are you flying by the seat of your pants? Time to get grounded. A haphazard deworming program puts him at risk for increased exposure to parasite eggs and larvae.

My simple, two-step guide will help you design a top-notch deworming program that's best-suited for your horse. The first step helps you decide whether to put him on a periodic ("purge") program, or give him a daily dewormer with his feed. The second step covers three parasitic "troublemakers" that aren't always killed by a general dewormer. Then I give you tips on how to stick with the program you select. Finally, I detail two day-by-day sample deworming programs, and give you the rundown on six effective dewormers.


First, decide whether to put your horse on a periodic ("purge") program with a paste dewormer or give him daily dewormer in his feed. To help you determine which program is right for your horse, I'll briefly explain a worm's life cycle, then how each deworming program works to interrupt that cycle. Next, I'll give you a short quiz to help you determine your horse's specific needs.

A worm's life cycle: Your horse ingests most worms that plague him as larvae. Some of these larvae (such as large and small strongyles) migrate through his body tissues and end up in his gut, where they mature and lay eggs. He then passes these eggs in his manure, where they hatch into larvae and spread into the environment. He ingests the larvae, and the cycle is repeated.

How a purge program works: It breaks the cycle primarily by killing adult worms before they lay eggs in your horse's intestines. By reducing the number of eggs, it'll minimize his exposure to parasites-unless he shares grazing space with other horses on less-than-effective deworming programs. If you choose this option, rotate different classes of deworming medication. Cost: About $80 per year.

How a daily program works: It kills the early-stage larvae your horse picks up in his mouth before they penetrate his body tissues. Once larvae start migrating through his body, they can cause damage. So, by killing them before they begin migrating, daily dewormers minimize his internal parasite levels even if his environment is heavily infested and/or out of your control. Cost: About $144 per year.

QUIZ: Now see how you score on the following eight questions to determine which program is right for your horse.

1. Does your horse graze on pasture all year, increasing his chances of exposure to parasite larvae? (Yes=2. No=0.)

2. Do other horses, on different or unknown deworming programs, graze on the same pasture, increasing your horse's chances of ingesting parasite larvae? (Yes=3. No=0.)

3. Does your horse nibble grass at other stables or public horse facilities-such as show grounds, fairgrounds, campgrounds, and/or highway rest stops-increasing his chances of ingesting parasite larvae? (Yes=5. No=0.)

4. Has your horse ever shown signs of heavy worm infestation? (Symptoms include a poor haircoat, weight loss, recurrent colic, or sloppy manure; or a fecal egg count of more than 100 eggs per gram.) (Yes=4. No=0.)

5. Is the collected manure at your horse's facility spread on the pasture as fertilizer, increasing the chance of parasite larvae in his grazing pastures? (Yes=3. No=0.)

6. Is "dropped" manure in your horse's grazing areas spread out with a harrow at least once a year? (Yes=3. No=0.)

7. Do you have a hard time keeping track of which dewormers can be used in a rotation program-possibly disrupting a purge program?(Yes=2. No=0.)

8. Do you delay scheduling your horse's regular-care appointments, such as farriery, dentistry, vaccinations, and deworming? (Yes=3. No=0.)

Here's what your total score means.

0-8: Your horse's management and general condition are good enough that a well-timed purge program probably is adequate. It'll minimize parasite eggs in his manure, and his risk of internal damage from worm larvae picked up in the environment is probably minimal. (Exception: If you answered "yes" to questions 3, 4, and/or 5, risk of damage increases; consider a daily dewormer.)

8-15: You're in a gray area. Although a well-timed purge program will minimize worm eggs in your horse's manure, other factors- such as a high concentration of parasite larvae in his environment- may expose him to internal damage.

15-25: Your horse is exposed to high levels of parasite eggs and larvae in his environment. Use a daily dewormer to protect him from internal damage caused by larvae migration.


Whether you choose purge or daily deworming, you won't kill some dangerous parasites unless you take additional steps. These troublemakers are bots, tapeworms, and encysted cyathostomes (one of the most destructive immature forms of small strongyles). Here's a general program to fight these parasites, but check with your vet to develop a program right for your horse and your particular area.

Bots. Ivermectin and moxidectin are the only available products effective against bots. In a purge deworming program, you can kill two birds with one stone by using one of these products on your regular late-fall and spring treatment dates. Time of year is critical, because fall's' first frost kills bot flies, giving you a leg up on reducing their population-especially if you follow up in the spring. Here's what to do: After first frost, remove/kill any remaining bot eggs or larvae on your horse's legs with a bot block or knife. Then use a purge dewormer to get rid of adult bots in his system. In spring, remove/kill any external eggs or larvae you may've missed in the fall, and deworm him again to zap any adult bots in his stomach before they lay eggs. Then you'll start bot season (spring through early fall) with a clean slate.

If your horse is on a daily program, give him a dose of ivermectin or moxidectin in early spring and again in late fall, in addition to the daily dewormer.

Tapeworms. Some investigators believe daily deworming effectively controls tapeworms, but the evidence is conflicting. As an extra measure, you have three options: 1) give pyrantel pamoate (Strongid P or T), at twice the usual dose, 2 days in a row; 2) give pyrantel tartrate (daily dewormer), at 10 times the usual daily dose, 2 days in a row; or 3) use of the canine tapeworm medication prazi-quantel (Droncit), which your vet can prescribe for oral use in your horse (about $45 a dose). You can use options one or two to replace your horse's regular deworming treatments in spring and fall. Give Droncit in addition to the regular deworming treatment, but on a different day, to avoid possible drug interactions.

Encysted cyathostomes. Prevent encysted cyathostomes by putting your horse on a daily deworming program, or kill them by: 1) using moxidectin as a spring and/or fall treatment in your purge deworming program; or 2) replacing a regular spring and/or fall purge treatment with fenbendazole at twice the usual dose, for 5 days in a row.



  • For daily programs, it's critical that your horse gets his daily dose daily, as missed doses will decrease the levels of dewormer in his system, rendering it less effective.

  • For purge programs, timing is key. If you treat too early, targeted worms will be too immature to be affected by the dewormer. If you treat too late, adult worms will have the opportunity to produce eggs, infesting your horse's environment and raising his (and other horses') risk of exposure.


Here are my four stick-to-it tips.

1. Buy the whole year's worth of dewormer at once. If you don't have it on hand, you may miss a critical deworming date.

2. Label each tube with each horse's name and the date to be given.

3. Keep your dewormers handy. But store them out of reach of children and pets.

4. Post a calendar prominently in your barn. On it, clearly mark the day before each deworming day to give you time to prepare. On the scheduled day, set out your dewormer where you can't miss it.

Karen Hayes is an Idaho-based equine practitioner.

This article first appeared in the June 1999 issue of Horse & Rider magazine.


Parasite Control
by Madalyn Ward, DVM


Strongyles (Blood Worms)

For many years it was thought that the large strongyles were the only real threat to horses' health. The large strongyles caused considerable damage to the blood vessels supplying the intestine during the migration stage. The damage caused by migrating large strongyles caused many horses to become chronic poor doers or colickers.

With the introduction of avermectin-type dewormers that killed migrating strongyles, the danger of permanent damage to blood vessels was greatly decreased. However, horses continued to colic and do poorly and we began to realize that the small strongyle species was equally damaging although in a different way.
The small strongyles penetrate the wall of the intestine and become encysted there until conditions become favorable for them to emerge. These encysted larvae are resistant to dewormers, even the avermectins that kill migrating large strongyles.

Large and small strongyles are resistant to many dewormers on the market today. My drug of choice is Strongid pasteT (pyrantel). This is a very safe product that has been on the market for years and has a proven track record. In healthy horses it stays in the digestive tract where it kills the adult worms. It is not absorbed systemically. IvermectinT, ZimectinT, or QuestT (avermectins), on the other hand, are absorbed, which allows them to kill migrating parasites but also increases their toxicity. StrongidCT (pyrantel tartrate) is designed to be fed on a daily basis to kill worm larbae as they are ingested and to kill small strongyles as they emerge from the gut wall. Most small strongyles are resistant to benzimidole dewormers such as PanacurT.

Ascarids (Roundworms)

These worms are rarely a problem in horses over 2 years old. They can, however, be deadly for youngsters. After the ascarid eggs are ingested, they migrate through the liver and lungs. Many of the "colds" and coughs of babies are actually related to the inflammation in the lungs from roundworm migration. The adult worms can become quite long, and in large numbers cause blockage of the intestine. Roundworms in the intestine are killed by pyrantel, avermectin, and benzimidole dewormers. Avermectins are reported to be effective against adult and migrating ascarids, but based on my experience, I prefer pyrantel or benzimidoles.


It has been thought that tapeworms do not cause much damage to horses, but recently they are being looked at more closely. Tapeworms attach to the intestine at the junction between the small intestine and cecum. This is already a potential area of impaction in the horse, and it is believed by some that tapeworm infestation compounds the problem. Unfortunately tapeworm eggs do not show up on routine fecal exams, so if regular deworming is not resulting in thriftiness, consider giving pyrantel at 2-3 times the normal dose; this should kill any tapeworms.

Oxyuris (Pinworms)

These worms do not cause serious disease but can be irritating to horses. Stabled horses are most at risk. The female worm lays eggs around the perianal area, causing the horse to show symptoms of tail rubbing and hair loss. The best treatment is to wash the area with a mild soap and apply a soothing ointment.


These worms cause mild diarrhea in young horses. Foals become infected via the mare's milk. Benzimidazole dewormers are safe and effective to use to treat foals. Control involves removing moist damp bedding where the worms breed.


These are not worms at all, but fly larvae. The female botfly, which looks like a bee, lays eggs around the face or legs of the horse and the eggs hatch when exposed to moisture. The larvae migrate to the stomach and attach there to develop. The larvae cause little damage, but the flies are extremely irritating to horses. Avermectin-type dewormers are excellent for controlling bots and treatment is only needed if the small yellow eggs are seen on the legs. Wetting the eggs with warm soapy water or scraping them off the hair is an easy, non-chemical approach to bot control.



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