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Parasite Management Overview

Parasites have an unnerving relationship with humans and their domesticated animals; horses in this reference. This parasitic relationship is deeply rooted in our mutual histories. Parasites have a natural advantage that makes it almost impossible to permanently eradicate them; they adapt. Modern drugs are somewhat effective until they adapt and become resistant that that drug. We can, at best, keep them at bay with a well thought out regimen. Some steps to reduce parasite infestation include:

  1. Manure Removal - Regularly removing droppings from the horse's stall, shed or field and a good mitigation plan
  2. Avoiding Crowding in turn out paddocks (turn out).
  3. Resting Paddock - Periodically ‘resting’ (Keeping horses off this paddock) a paddock for several weeks.
  4. Bot Flys  - If botflies are active, fly spray may repel insects, but needs frequent reapplication to remain effective.
  5. Bot Fly Eggs - A small pumice stone or dull knife may be carefully used to scrape off any Bot Fly eggs that are stuck on the horse. (Bot eggs are yellow and roughly the size of a grain of sand, they are clearly visible on dark hair, harder to spot on white hair.)
  6. Wormers - using the above steps will not completely eliminate parasites. Therefore, most owners commonly give anthelmintic (wormers) drugs to their horses to reduce these parasites. (Click Here to See a Parasite Worming Chart)

Wormer Drug Delivery Methods: Wormers come in several forms, including pastes, gels, powders, and granules or pellets. Powders and granules normally come in single-dose packaging, and the wormer is normally mixed in with the horse's feed. Pastes and gels normally come in a plastic syringe which is inserted in the side of the horse's mouth and used to squirt the wormer onto the back of the horse's tongue. (Click Here to See a Parasite Worming Chart)

Methods of Worming: There are two common methods of worming

  1. Purge Wormers.
  2. Continuous (Daily) Wormers.

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.
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. (Click Here to See a Parasite Worming Chart)

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. (Click Here to See a Parasite Worming Chart)

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. (Click Here to See a Parasite Worming Chart)

Risks Surrounding Worming: Modern anthelmintics are quite effective against worms. 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, such as Panacur, or a low-dose daily wormer for the first month or so, and then follow with periodic purge wormer treatments. (Click Here to See a Parasite Worming Chart)
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. (Click Here to See a Parasite Worming Chart)

Types and Species of parasites found in horses.
Ascarids (Parascaris Equorum): (Click Here for More Information)
Bot Fly (Gasterophilus spp): (Click Here for More Information)
Lung Worm (Dictyocaulus arnfieldi):
Pinworms (Oxyuris equi): (Click Here For More Information)
Large Strongles (Strongylus vulgaris):. (Click Here For More Information)
Small Strongles (Strongyles Trichonemaspp): (Click Here For More Information)
Ringworm: Ringworm in horses is not actually a worm but a contagious fungal skin disease and is normally treated using an anti-fungal wash.
Tapeworms (Anoplocephala perfoliata): (Click Here For More Information)
Threadworms (Strongyloides Westeri): (Click Here For More Information)

Parasitology Products - Anthelmintics or chemical wormers.
(Note diagnosing horses requires veterarinan consultation Click Here For A List of Florida Veternarians - Note the use of chemical wormers on foals under 4 months is not recommended) (Click Here to See a Parasite Worming Chart)

Ivermectin (Click Here to See a Parasite Worming Chart)
Moxidectin(Click Here to See a Parasite Worming Chart)
Praziquantel(Click Here to See a Parasite Worming Chart)
Pyrantel(Click Here to See a Parasite Worming Chart)
Fenbendazole(Click Here to See a Parasite Worming Chart)