Equestrian Outreach Parasite Treatment Page

Purge Wormers: Purge wormers kill parasites with a single strong dose, are given periodically, usually every 8–12 weeks, depending on local conditions and veterinary recommendations. (Click here for a list of Florida Veterinarians)
Continuous (Daily) Wormers: Continuous wormers are given in the horse's feed each day, in small doses, and kill worms as they infect the horse. Neither of these methods is perfect; purge wormers are effective for rapidly killing all parasites, but are gone from the horses' body in a few days, and then the horse may start to be re-infected. Continuous wormers are a mild low dose and may be easier on the horse, but may not be effective in quickly killing worms in a heavily-infected horse, and may contribute to drug resistance.
Wormer Rotation: No single wormer drug will kill all types of worms, so horses normally require a assortment of wormers and a pleathera of worming strategies such purge worming with a different drug on a rotating basis, at least 2 or 3 times per year.
Wormer Resistance: Many horse owners also rotate between the different chemical classes of wormers to combat the tendency of parasites to develop resistance to a given class of drugs. (If a treatment doesn't kill at least 95% of a worm species, that species is classed as 'resistant' to the drug.) Another way of combating drug resistance is to worm less frequently, by having manure samples tested for the presence of parasite eggs and then worming only when the count gets high enough, and with a wormer specific for the type of worm eggs found. However, this method is not entirely reliable, as the parasite load varies somewhat with the seasons, and some parasites (such as bots) may not show up in a fecal egg count at all.
Risks Surrounding Worming: Modern anthelmintic (chemical wormers) drugs are effective against worms if used prudently. However, if a horse is heavily infested with parasites, wormers must be given carefully. A horses' body may be overwhelmed by the toxins released by a heavy load of dead worms after worming with a powerful drug. There have been documented cases of horses, particularly if also undernourished, ill, or otherwise weakened, to become sick or even die. Thus, a veterinarian may recommend worming with a mild class of drugs, or a low-dose daily wormer for the first month or so, and then follow with periodic purge wormer treatments.
Seasonally Targeted Parasite Regimens: There are several different brands of wormer, using different types of active chemical - which in turn kill different types of parasites. It is sometimes necessary to use a specific wormer at a certain time of year, depending on the life cycle of the parasites involved. Many horse owners rotate wormers during the year, using different brands or formulations with different active chemicals, to combat drug-resistant parasites.
Worm Tests: As a part of a careful worming resistance avoidance regimen. Limiting the treatment frequency and the regular monitoring of feces and blood for parasitic symptoms. Fecal egg counts (FECs) should be performed in the laboratory. Check for anthelmintic resistance. Ensure the treatments you use are effective, (consult your vet).
Identify and selectively treat wormy horses. These horses tend to be 'carrier animals' and routinely may have high fecal egg counts that contaminate your paddocks and so infect other horses.

Individual Horses - greater than 400 eggs per gram
Herd Test (minimum of ten horses) - 200 eggs per gram

(Note diagnosing horses requires veterinarian consultation - (Click here for a list of Florida Veterinarians)

Anthelmintic or Chemical Wormers
(Note diagnosing horses requires veterinarian consultation) (Click here for a list of Florida Veterinarians)

(Note the use of chemical wormers on foals less than 4 months is not recommended)

Ivermectin: Ivermectin is widely accepted and used on horses. It is generally delivered orally in paste form. Ivermectin is considered to be anywhere from 90 to 100 percent effective against most internal parasites, except tapeworms and encysted small strongyles. Ivermectin works as a neuromuscular agent, disrupting biological functions within the parasites; generally with no ill effects to the animal. However the popularity of Ivermectin also holds the potential of overuse and the resulting parasite resistance. A rotation regimen is recommended. (Click Here for More Information)
Moxidectin: Moxidectin, another neuromuscular worming drug. It is generally delivered orally in paste form. Moxidectin is considered to be as effective as Ivermectin in controlling a wide range of parasites (Not Tapeworms) and has the added advantage of being effective against encysted small strongyles and is effective up to 45 days longer than Ivermectin.
Praziquantel: Praziquantel is a member of the pyrozine group of de-wormers that is effective against cestodes which is the family of helminthes called tapeworms. There are three species which infect horses and horses only: Paranoplocephala mamillana, Anoplocephala magna, and Anoplocephala perfoliata. As we learn more about tapeworms, our understanding grows that they are an important cause of both medical and surgical colic cases in equines.
Pyrantel: (Pyrantel Pamoate and Pyrantel Tartrate) Delivery comes in two forms Pyrantel Pamoate as an oral paste and Pyrantel Tartrate as a daily feed supplement. Both forms of Pyrantel work as neuromuscular agents, disrupting biological functions within the parasites; generally with no ill effects to the animal. They are about 90 % effective against Tapeworms and somewhat less effective against Strongylus (Large & small round worms), Pinworms but not the Bot Fly. However the popularity of Pyrantel also holds the potential of overuse and the resulting parasite resistance. A rotation regimen is recommended.
Fenbendazole: Fenbendazole is part of the Benzimidazole family of drugs. Fenbendazole is effective against Strongylus (Large round worms and less effective against small round worms), Pinworms but not the Bot Fly. Fenbendazole works by disrupting biological functions within the parasites causing starvation. There is increasing evidence of resistance to this drug and a rotation regimen is recommended.

Equine Parasite List:

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