Rethinking Deworming

by: Joyce Harman, D.V.M., M.R.C.V.S.

Equine deworming is going through a transition in the conventional veterinary world. Craig R. Reinemeyer, D.V.M., Ph.D., has been studying equine parasites, parasite resistance to anthelmentic drugs and better ways to control parasites for many years. Finally, his work is becoming mainstream; however, it will still be many more years before the horse world changes its longstanding habits permanently. Equine deworming has been done using a six to eight weekly rotation schedule of anthelmentics for three decades. Parasite resistance has been identified with many of the drugs in current use and there are no new classes of drugs on the horizon.

The adaptation of Dr. Reinemeyer’s earlier work is refreshing. Fecal eggs counts are performed on a regular basis to determine which horses on a farm shed eggs and which ones do not, or which have low counts. Deworming is only performed on those horses that show a need. Drugs available fall into three classes: macrocyclic lactones–ivermectin and moxidectin; benzimidazoles–fenbendazole; and pyrimidines–pyrantel. Resistance had been shown in all classes. If drugs are used, the ones that should be selected are those that do not have resistance on that farm. Natural deworming compounds can be substituted, without the resistance problems and environmental concerns surrounding the use of drugs.

Extensive drug use on a farm results in contamination of the soil with drug residues as well as parasite resistance.

Many horse owners as well as veterinarians consider that the only acceptable level of parasites is zero. However, parasites evolved in nature to co-exist with a host. If the host is dead, the parasite is without a home, so the most successful parasites have a non-destructive relationship with their hosts. Wild horses (and other animals) around the world have never received chemical deworming yet they survive, reproduce and raise young. How wild horses naturally control parasites can help determine better management practices for domestic horses.

The parasites that people are concerned about are the small strongyles, since the large strongyles common before modern anthelmentics came into use have been basically eliminated. Large strongyles did cause serious and devastating colic’s. Small strongyles, however, are not much of a clinical problem, unless the horse is in extremely poor condition and has a heavy parasite load.

Parasites become a problem for the domesticated horse for several reasons besides drug resistance. One of those is that confinement produces a certain low level of stress in the equine that can affect the immune system, allowing parasites to overpopulate in the animal. Even wild animals whose natural range is decreasing experience this. Horses are social animals that live in a herd, moving and eating 20 hours a day compared to domestic horses that may live in single stalls or paddocks, not moving much and having food rationed to certain times of the day.

Wild horses range over a large area and therefore do not graze around the “roughs” or areas where manure has been put and parasite eggs hatch into larvae. Horses in confinement are often forced to graze close to or in an overgrazed pasture, directly on those long clumps of grass harboring larvae.

Wild horses have a healthy gut ecosystem of beneficial bacteria and other microorganisms where the parasites can live in balance. Modern horses often have been treated with antimicrobials and other drugs that have a negative effect on the gut ecosystem as well as the immune system, which leaves the horse more susceptible to parasite overload.

The approach to deworming from a holistic perspective needs to use management changes on the farm, fecal egg count checks and the use of natural products to decrease the parasite load in the pasture. The goal of modern deworming is to control the parasite load in the pasture through management and the identification and treatment of individual horses that shed high levels of eggs into the manure. Treatment of those individuals with high egg counts can then be done using natural deworming agents. It has been this author’s experience that horses in high stress, competitive environments who are shedders of eggs are harder to control with natural treatments, due to the ongoing levels of stress. Drug treatments may need to be done periodically.

Management changes in confinement situations include the removal of manure on a regular basis. Composting is the best way to remove the eggs from the environment, while spreading manure in pastures just carries the eggs around the farm to increase the exposure to all horses. Manure can be broken up by harrowing during hot, dry weather (over 90 degrees), or during pasture rotation when the horse is off the pasture. This will allow the eggs to hatch and the larvae to dry up before ingestion by the horse. Freezing does not kill the eggs, so do not break up the manure during the winter and definitely not in the spring and fall.

The next step is to check fecals on all the horses. Identify the high and low shedders. To establish a baseline for a horse or group, it is necessary to check fecals on a regular basis throughout the year, at least quarterly. Horses that consistently have similar eggs counts through the year can be placed onto a list of shedders, non-shedders and those in between. To obtain the highest egg count, ancient cultures have found the highest levels around the full moon.

Horses that consistently show a low or negative egg count can be listed as non-shedders and do not need to be dewormed with any product. Some horses never need to be dewormed! Horses with a moderate egg count should be dewormed until the count drops to the low range and stays there for several fecals. These horses can contaminate the pasture.

After using a deworming product, check the fecals again in 10 to14 days to be certain the protocol worked. The egg count should be at least 90 percent decreased. Horses that are shedders should be rechecked in about six to eight weeks and dewormed again if needed. When parasite loads are high, it may be necessary to use chemical dewormers until the situation is under control. High shedders may benefit from a five-day dose protocol of Panacur®, which clinically seems to be the safest larvacidal deworming protocol in this author’s practice.

Natural deworming compounds can be used in many cases. If the horses are under stress or are living in heavily contaminated properties, natural methods may not work, or may need to be supplemented with chemicals at times. Many companies sell products claiming 100percent efficacy from their product. This is impossible knowing the complexities of the living horse and environmental issues. It is also impossible for a natural product to be given as a single dose and to expect it to be strong enough to clear parasites in a similar manner to a single drug dose.

Probiotics and prebiotics help restore the natural balance of healthy bacteria in the gut. In creating a natural health program for a horse, a two- to three-month course of these should be considered. Horses that have been ill, have poor immune systems or have been treated extensively with antibiotics may need to use these products routinely. There is no harm in long term use of pre- and probiotics as long as they contain natural ingredients and no preservatives.

Natural deworming is usually done with herbs, homeopathics or mechanically with diatomaceous earth (DE), a fine powder from the shells of diatoms or microscopic algae. The edges are very sharp and act mechanically to slice the outer skin of the parasite, adult, egg or larvae. It can actually absorb moisture from the parasite into its fine structure. Once this occurs, the parasite dies. There is no chance of resistance, since it is a mechanical damage. There is some theoretical concern about intestinal irritation, but that has not been clinically apparent in many years of using products containing DE.

Diatomaceous earth is often mixed with vermifuge herbs. This can enhance the effectiveness of the product. DE can also be offered free choice to horses, and in many cases, but not all, horses will eat the DE usually just before the full moon as the parasites are becoming more active. One such product mix is MOP., by Advanced Biological Concepts®.

There are many herbs that have an anthelminitic or vermifuge action. Some are relatively harsh or slightly toxic and should be used for short periods of time or mixed with herbs that soothe the digestive tract, such as marshmallow, sustainably harvested slippery elm or herbs that help prevent cramping such as chamomile or valerian. Some herbs are contraindicated in pregnancy. Any herbal formula that is purchased should be formulated by a well-trained, experienced equine herbalist, not a well-intentioned horse person who has looked up herbs that clear parasites.

Some of the herbs that have vermifugal actions include:

  • Garlic (Allium Sativum)
  • Peppermint (Mentha Piperita)
  • Common Thyme (Thymus Vulgaris)
  • Cinnamon (Cinnamomum Zelandicum)
  • Echinacea (Echinacea Augustifolia)
  • Quassia (Picrasma Excelsa)
  • Tansy (Tanacetum Vulgare)
  • Cayenne (Capsicum Minimum)
  • Fennel (Foeniculum Vulgare)
  • Cleavers (Gallium Aperine)
  • Nettle (Urtica Dioica)
  • Slippery Elm (Ulmus Fulva)
  • Elecampane (Inula helenium)

Classical, Single Remedy Homeopathy

  1. Uses homeopathic remedies in the drinking water
    a. Use a water tub or bucket, not just stream through the field
  2. Select 2 to 3 remedies from the list below that apply to your situation:
    a. Tapeworms
    Granatum 3X — any age
    Cina 3X –young horses
    Chenopodium 3X — mature horses
    b. General worms — Strongyles
    Santonium 3X
    Cina 3X — best used with young horses
    c. Ascarids — usually just in young horses
    Abrotanum 3X
  3. To use:
    a. Add 1 pellet of each remedy selected per gallon of water
    (in a 5-gallon bucket: 3 remedies = 15 pellets altogether)
    b. Change the water daily — if using a large tub, fill only what they will drink in 1 day
    c. Use remedies for 5 days each month at the time of the full moon

Combination Homeopathy
EquioPathics WRM Clear®, (manufactured by Washington Homeopathic Products for EquioPathics, LLC ) needs to be administered for 3 weeks during the initial course. Homeopathics do not kill parasites, they improve the health of gut, so the parasites do not wish to live there.

Chinese Herbal Deworming
The Chinese have used herbal dewormers for centuries. Formulas are not readily available but many veterinarians who practice Chinese medicine have products available for the stubborn cases. Many of the Chinese herbs are capable of killing or driving out the parasites, but also a well-made formula can help support the immune system of the gut.

To contact the author:
Joyce Harman D.V.M., M.R.C.V.S.
Harmany Equine Clinic, Ltd.
Flint Hill, Virginia

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