Deworming Your Horse 101

By March 6, 2017 Uncategorized

Internal Parasites: Strategies for Effective Parasite Control

Based on article from the AAEP

Internal parasites, or worms, can be silent thieves and killers.

In terms of management priorities, establishing an effective parasite control program is probably second only to supplying the horse with clean, plentiful water and high-quality feed. It’s that important!


Contrary to popular belief, horses can have large numbers of internal parasites while still appearing to be relatively healthy. But in some individuals, especially young horses, parasites can take a visible toll. Common signs of parasitism include the following:

• Dull, rough haircoat

• Lethargy (decreased energy) or depression

• Decreased stamina

• Unthriftiness or loss of condition

• Slowed growth in young horses

• Pot belly (especially in young horses)

• Colic

• Diarrhea




Having your veterinarian perform fecal egg counts to determine the amount of egg shedding that your horse has is important. This information will help ensure that the dewormers that are being used are effective and also help determine the frequency of deworming necessary to keep your horse healthy.

It is important to note that a negative fecal examination does not mean the horse is free of internal parasites. Some types of parasites produce eggs only intermittently. Larvae do not produce eggs at all, and may be present in large numbers in a horse with a fecal egg count of zero. And tapeworm eggs may be missed with routine fecal egg count techniques. The results are most useful when several horses on a farm are tested on the same day. This information gives the veterinarian and farm manager a good idea of the level of parasitism on the property.


There are several different dewormers, or anthelmintics, currently available. No deworming product is 100 percent effective in ridding every horse of all internal parasites. However, it is not necessary for a product to kill every worm in order to improve the horse’s health, minimize the risk of serious disease, improve feed efficiency, and reduce pasture contamination with parasite eggs and larvae. As mentioned above, resistance has developed against several of these dewormers in both small strongyle and roundworm parasites. It is therefore of utmost importance to routinely test the effectiveness of a given dewormer on every horse establishment.

Methods of Administration

There are two main ways of administering dewormers:

• Oral paste syringe

• Feed additive (powder, liquid, or pellets)

Both methods are effective, provided the proper dose is given at the right time, the horse receives the full dose, and resistance has not developed in the parasites being targeted. The dose must be calculated based on the horse’s body weight. Weight tapes are an accurate enough way of estimating a horse’s body weight for this purpose.


There is no single deworming program that suits all horses and all situations. The ideal program for your horse(s) depends on number and ages of the horses on your farm, pasture management and your geographic location. It is best to have your regular veterinarian help you devise an appropriate deworming program for your horse or farm.



Chemical control using dewormers is just one part of a complete parasite control plan. As parasites are primarily transferred through manure, good management is essential. Some of the procedures listed below can be helpful in reducing parasite burdens:

• Keep the number of horses per acre to a minimum to prevent overgrazing and reduce pasture contamination with parasite eggs and larvae

• Pick up and dispose of manure regularly (at least twice a week during the warmer seasons, even in dirt or sand yards)

• Do not spread manure on fields to be grazed by horses; instead, compost it in a pile away from the pasture before spreading it out

• Mow and harrow pastures periodically to break up manure piles and expose parasite larvae to the elements (larvae can survive freezing, but they cannot tolerate extreme heat and drying for very long)

• Consider rotating pastures by allowing sheep or cattle to graze them, thereby interrupting the life cycles of equine parasites

• Use a feeder for hay and grain rather than feeding on the ground

• Remove bot eggs regularly from the horse’s haircoat (flea combs work well in some instances)

• Consult your veterinarian to set up an effective deworming program for your horse(s) and monitor its effectiveness.

For more information on parasites and deworming, contact our office, or click HERE to read the protocol on our website.

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