Which is the Best Horse Dewormer?

With so many dewormers available in the market, it can be confusing to determine which one is best for your horse.  In this article, we will take a closer look at the factors to consider when selecting a dewormer for your horse. 

Deworming, also known as worming, is an essential part of your horse's healthcare program.  Deworming is used to control your horse's internal (and some external) parasites that can contribute to serious respiratory, digestive, and performance health problems.

Deworming or worming consists of orally administrating an Over the Counter (OTC) chemical substance formulated to stun, paralyze or kill your horse's internal parasites.

Equine Parasite Control Programs

However, deworming alone only targets your horse's parasitic infection.  Therefore, horse deworming should be used in conjunction with a parasite control program that provides ongoing protection from both parasitic infection (the parasites currently inside your horse) and reinfection (the future parasites that your horse will be exposed to).  

The goal of an equine parasite control program is to control your horse's internal parasites, not eliminate them.  Following a parasite control program:

• allows you to use fewer unnecessary chemicals.
• provides ongoing infection and reinfection protection.
• is better for the environment.
• will help slow down parasitic resistance on your property.

A comprehensive parasite control program consists of testing, treating, and managing your horse's exposure to parasites. For more information on horse parasite control programs, check out the following article -> Which Deworming Program is Right for your Horse?

Which Parasites Should I Deworm For?

No horse is completely immune to parasites.  Parasites affect all breeds, types & ages of horses.  In fact, there are over 150 types of parasites that can infect your horse.  The most common internal parasites include:

• Redworms (Small Strongyles/Cyathostomins
• Roundworms (Ascarids)
• Pinworm
• Bots
• Tapeworms (Flatworms)
• Bloodworms (Large Strongyles)
• Hairworms
• Stomach Worms
• Lungworms

Some of these parasites take a significant toll on your horse's digestive system causing indirect damage such as nutritional deficiencies, anemia, or colilc and if left untreated cause direct damage such as inflammation, ulcers, or tissue death.

**** ADULTS ONLY ****

It's worth noting that most horse dewormers are only effective against adult parasites that are present inside your horse's digestive tract and therefore do not address a significant portion of a parasite's lifecycle (i.e., the egg, larvae, migrating, and encysting stages).

Test Before You Treat

Prior to deworming or worming your horse, you should identify the type and number of parasites infecting your horse by performing a fecal egg count test.  Fecal egg count tests not only help identify the type of parasites to target with your dewormer but also indicate how well your dewormer is working.  For more information about fecal egg count tests, check out the following article -> What is a fecal egg count test?  

Treat According to Results

Since dewormers or wormers are formulated to control specific parasites, knowing the type of parasites infecting your horse allows you to select a dewormer that targets those specific parasites.  For example, if roundworm eggs were discovered in your horse's fecal sample, then you would purchase a horse dewormer effective against roundworms.

Following is a list of factors to consider when selecting a dewormer:

• Product: No dewormer is effective on all equine parasites.  Specific dewormers target specific parasites.
• Species of parasites: Different species of parasites react differently to different dewormers.  A fecal egg count test can help identify the types of parasites infecting your horse.
• Frequency:  How often you treat your horse should be dictated by their parasite burden classification of High, Medium, or Low, which should be available on your horse's fecal egg count test results.
• Age: Each horse's immunity to parasites uniquely develops as they age; therefore, different dewormers may be needed throughout your horse's lifespan.  For example, younger horses may require a different drug classification of dewormer or more frequent deworming compared to mature horses.
• Health: You should evaluate your horse's ability to withstand the stress of deworming prior to administering a dewormer or wormer.
• Climate & Timing: Parasites tend to breed when their offspring have the highest chance of survival.  I refer to this as the Goldilocks syndrome.  Parasites do not like it too hot, too cold, too dry, or too wet - they like it just right.
• Management Practices: Such as turnout, grazing habits, and herd management expose your horse to the risk of potential parasite infection.  Make sure all your horse's areas are clean and free of manure whenever possible.
• Dewormer Resistance:  Overuse of dewormers causes the parasite population to become resistant to those products.  It's important to use dewormers as part of a compreshensive parasite control program   that targets deworming based on only the type(s) of parasite infecting your horse.
• Parasitic Refugia:  Refugia is when you purposely do not expose some parasites to a dewormer, essentially giving them refuge.  This approach slows down the parasite population's resistance to that drug class.  For example, you could choose to only treat the medium or high-shedding horses while leaving your low and zero shedders untreated.

Only 3 Left to Defend

You may find it surprising that although there are dozens of dewormer brand names, there are only three different chemical classes of equine dewormers available to the consumer without a prescription.  Also surprising is that there is no new chemical deworming drugs in development.

Due to decades of overuse, some species of parasites are becoming resistant to certain deworming drug classes.  Therefore, we should use these remaining three classes of drugs as sparely as possible to slow down resistance. 

Each of these three chemical classes represents a family of drugs which uses a different mode of action (i.e., stuns, paralyzes, or kills) to control targeted parasites. All three drug classes are represented in Table A1 under the column heading of DRUG CLASS (e.g., Benzimidazoles).

Table A1 - Horse Dewormers Available in the United States

Each drug class also goes by a generic name (e.g., Moxidectin).  The generic name is listed under the column heading GENERIC.  Each generic drug has a variety of brand names under which they are sold.  Some more popular brand names are listed under Table A1's column heading BRAND NAME. 

All brand names listed in Table A1 are currently available as an OTC medicine and can be found online at most equine e-commerce websites -> view the latest sales here or local tack shops and feed stores.  Finally, Table A1's last column on the right, labeled TARGETED PARAISTES, lists the parasites that each drug class is labeled to be most effective against (i.e., small strongyles).

The following is an explantation of each drug class and the parasites each class targets.

Benzimidazoles (BZs) or the “azoles”

Nicknamed BZs, this class of drugs includes equine dewormers ending in "azoles' – like fenbendazole.  The members of this drug class are considered broad-spectrum dewormers and are therefore labeled as effective against a wide range of internal horse parasites.  Using the proper dosage administered over multiple days allows BZs to remain effective inside your horse for an extended period of time which increases the drug's effectiveness against some of the targeted late-stage larvae and parasites (e.g., encysted small strongyles).  However, some research shows that small strongyles are developing a resistance to BZs.

BZs can be administered using an oral paste or as a topical feed dressing additive and are safe for use in most horses, including pregnant mares and stallions.  BZs that are approved for horse dewormers go by the generic names of fenbendazole and oxibendazole. 

Fenbendazole kills large and small strongyles, pinworms, and roundworms and (at double-dose for 5 days) kills migrating large and small strongyles, migrating ascarids and encysted small strongyles.  Fenbendazole's common brand names include Safe-Guard Paste, Safe-Guard Power-Dose, Safe-Guard Equibits, Panacur Paste and Panacur Power Pac.

Following are links to a couple of popular fenbendazole brands. Click on the underlined product names for more information.**

Macrocyclic Lactones (MLs) or the "mectins"

MLs or "mectins" are the most widely used of the three equine dewormer chemical classes.  According to their label, MLs are useful in controlling a wide range of internal horse parasites and are therefore considered broad-spectrum dewormers.  MLs can also control some skin-dwelling external parasites like lice, mites, and the larvae of parasites that cause summer sores.  Ivermectin and Moxidectin are the two most common generic MLs available for use in horses.  

Ivermectin's labeling states it is effective at controlling large and small strongyles, roundworms, pinworms, threadworms, large mouth stomach worms, bots, intestinal threadworms and lungworms.   Ivermectin is usually administered as an oral paste.  Ivermectin paste is available from several popular manufacturers, including Durvet, Duramectin, Bimectin, Zimecterin, Vetrimec, Horse Health, Promectin, and Ivercare.

Following are links to a couple of popular ivermectin brands. Click on the underlined product names for more information.**

Moxidectin is a more recently developed drug than ivermectin and is effective against large and small strongyles, encysted small strongyles, pinworms, roundworms, hairworms, lungworms, large-mouth stomach worms and bots.  Moxidectin also has the ability to penetrate into a horse's intestinal wall and therefore provides protection against some targeted parasites for a longer period of time after administration.  Therefore, unlike Ivermectin, Moxidectin is effective against late-stage encysted small strongyles.  This is especially useful for horses that are at high risk of parasite exposure.

Moxidectin is a more recently developed drug than ivermectin and is effective against large and small strongyles, encysted small strongyles, pinworms, roundworms, hairworms, lungworms, large-mouth stomach worms and bots.  Moxidectin also has the ability to penetrate into a horse's intestinal wall and therefore provides protection against some targeted parasites for a longer period of time after administration.  Therefore, unlike Ivermectin, Moxidectin is effective against late-stage encysted small strongyles.  This is especially useful for horses that are at high risk of parasite exposure.

Moxidectin is labeled for use in horses and ponies six months of age and older.  Moxidectin can be administered orally or as a paste, or topically as a feed additive.  Some common brand names for Moxidectin include Quest Gel, Equioxx, and Equest.

Following are links to a popular moxidectin brand. Click on the underlined product name for more information.**

Tetrahydropyrimidines (THPs)

THPs treat several worm species.  There are only two types of THP – pyrantel pamoate and tartrate.  Pyrantel pamoate is the compound in most commercial pastes and liquid deworming formulations, whereas pyrantel tartrate salt is the compound contained in topical feed dressing dewormers.  

Pyrantel pamoate controls large and small strongyles, roundworms and pinworms.  Some pyrantel pamoate brand names are Strongid Paste, Equi-Cide, Liqui-Care, TapeCare Plus and Pyrantel Pamoate Paste.

Following are links to a couple of popular pyrantel pamote brands. Click on the underlined product names for more information.**

Pyrantel tartrate is the basis of most topical feed dressing dewormers.  Pyrantel tartrate has a wide margin of safety and can be used on horses of all ages, from foals to seniors, including pregnant and nursing mares.  Pyrantel tartrate controls large and small strongyles, pinworms and roundworms.  Common names for Pyrantel Tartrate are Strongid C2X, Continuex and Equi Aid CW.

Following are links to a couple of popular pyrantel tartrate brands. Click on the underlined product names for more information.**

HONORABLE MENTION:  Praziquantel

Praziquantel belongs to a different drug class than BZs, MLs, or THPs.  Praziquantel is one of the few drugs that target and control tapeworm parasites.  Praziquantel, as on OTC, is only available in the US market in a combination paste with other drugs such as Ivermectin or Moxidectin.  A couple of brand names for these combination drug pastes are Equimax and Zimecterin Gold (Ivermectin/praziquantel) and Quest Plus Gel (moxidectin/praziquantel).

Following are links to a couple of popular combination drug brands that include praziquantel. Click on the underlined product names for more information.**

Where Can I Find Information About Which Drug Class is in a Dewormer?

The dewormer's packaging should display all the information regarding the product's drug class, generic and brand names as well as the type of parasites (indications) it controls.  Additional information on usage and administration instructions, ingredients, appearance, modes of action, dosage, storage, animal and human safety warnings

What Else Should I Consider When Deworming my Horse?

When deworming a horse, the following things should be avoided:

• Overdosing: Administering too much dewormer can be harmful to the horse and cause side effects.  Always follow the recommended dosages specified by the manufacturer.
• Overuse: Overuse of dewormers can lead to resistance, making them less effective.  It's important to use a targeted deworming program based on the parasite load of the horse and the environment.
• Improper storage: Store dewormers according to the manufacturer's instructions, as improper storage can affect their efficacy
• Unnecessary deworming: Each horse develops a unique immunity to parasites; therefore, not all horses need to be dewormed at the same frequency.  It's important to assess the parasite load of the horse and the environment to determine the frequency of deworming needed.
• Using the wrong dewormer: Different species of parasites require different types of dewormers.  A fecal egg count test can help identify the type of parasite present and determine the appropriate dewormer to use.

So what is the best dewormer for my horse?

In conclusion, choosing the right dewormer for your horse is important to your horse's health care program.  There are many factors to consider when selecting a horse dewormer, including the type of parasites present, the age and health of your horse, the recommended deworming schedule based on fecal egg count test results, the method of administration, and the risk of parasite resistance.

It is also important to note that other factors besides deworming to be considered when managing internal parasites in horses.  A comprehensive equine parasite control program should also include good management practices, such as proper sanitation, pasture rotation, and adequate nutrition, which also help to reduce the risk of internal parasite infections in horses.

Additionally, regular fecal egg counts can help determine the parasite burden level in your horse, allowing you to make informed decisions about when and how to deworm.  Finally, you should keep your veterinarian informed about your treatment program.  By working together, you can help to keep your horse healthy and control your horse's internal parasites, ensuring that they have the best possible quality of life.

**DISCLOSURE: Some of the links in this article are affiliate links, meaning at no additional cost to you, I may earn a commission if you click through and make a qualifying purchase.