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W-Thoughts on Worming

• If you choose to use chemical dewormers, do not use them in conjunction with other stresses, such as vaccinations or teeth floating–especially with tranquilization, not within a week before or after hauling or competing, don’t ride that day, or subject to any other type of emotional or physical stress. Obviously, you would not chemically deworm an animal running a fever or exhibiting acute or chronic disease processes such as heaves, hives, laminitis, etc. until the crisis is over or the acute situation is resolved.
• In terms of reported deaths and toxic reactions, Moxidectin leads the pack by a wide margin, followed by Ivermectin, then the Oxibendazole class, next the Pyrantel class, then Fenbendazole, and no reported deaths from Piperazine, Thiabendazole and Oxfendazole classes. These are listed in descending order, from the most dangerous to the safest, per The Horse Journal in October 2001.
• Support after chemical deworming with a probiotic for several days to help re-establish the beneficial gut bacteria, and consider using a pH balancer and detoxifier for a few days. Sometimes boarding stable or kennel rules or insurance companies dictate frequent worming, so these are some things you can do to support the horse in more quickly throwing off the toxic effects.
• If you choose to use daily wormer, consider giving the horse a break from the product during the winter months, when parasite activity and reinfestation chance is lower.
• Think carefully before deworming a particularly debilitated horse or dog. Many rescue cases go bad because of the rescuer’s frenzy to immediately deworm and vaccinate an animal that is already on its lips. A crisis may be avoided by waiting a few weeks until the animal has started to rally with proper diet and supplement support.
• If you are on a daily or semi-monthly deworming program and are seeing any of these side effects of liver toxicity, you may wish to back off on the chemicals and work on building up the animal:
1. Recurrent colics (especially right after deworming) or digestive distress, loose stools.
2. Weight loss, topline loss or muscle wasting.
3. Hypothyroidism as evidenced by weight loss or gain, crumbling hooves, laminitis, dry hair coat, frizzed hair coat, reproductive problems.
4. Hoof abscesses or white line disease.
5. Crabby attitude or lack of desire to work or play.
6. Muscle soreness, tying up or white, foamy sweat.
Any deworming or parasite control works best on a full moon! If you choose to do 28 days of an herbal or natural product you will automatically cover this. If you chemically deworm, do it at the full moon when the fluid pressure in the cells is at a peak, and you will get a better kill.
As a closing thought, remember that YOU have responsibility for the animals that have been given into your care. Research all possible angles, and don’t do anything out of fear or “because everyone is doing it.” Your veterinarian is your ally and (hopefully) friend, and you will find him/her supportive if you supply information and discuss these options that he/she may not know exist. Even the centuries-old herbal approach is new stuff to allopathically-trained practitioners. YOU are in charge of your health and that of your animals. See them as healthy and perfect, and consider all approaches before you make your own informed decisions! Twang some paradigms, if you have to…honor your instincts, listen to your animals.
Strategic timed deworming treatment should be given three times in the spring and fall one month apart as shown. The class of dewormer used can be interchanged as desired (see Section VIII). The last treatment should be given in late November or early December and may include both bot and tapeworm treatment if needed. Each “three-treatment strategically timed regime”  provides approximately six months of control thus the spring treatment protects the horses until fall and the fall regime protects the horses until spring. These repeated treatments also help remove encysted larvae which may have survived in the horse through the winter months while preventing more from establishing throughout the entire grazing season by reducing the overall build-up of infective larvae in the environment of the treated animals.
VIII. Equine Dewormers:
A. Equine dewormers currently on the market in the USA can be classified into
three separate classes of compounds based on the mode of action (See Appendix I):
These three major classes are: the benzimidazoles and pre-benzimidazoles (febantel,
fenbendazole, oxibendazole, mebendazole and oxfendazole), the macrocyclic lactones
(avermectin and moxidectin families), and the tetrahyo-pyrimidines (pyrantel). The mode
of action is different for each class of compounds. The benzimidizoles are non-soluble
compounds that destroy the metabolism of the parasites by interfering with the cell
functions in the parasites and by preventing the uptake of food thus starving the worms to
death. The macrocyclic lactones are very soluble compounds and affect the nervous
system killing the parasites causing a non-spastic paralysis while the pyrimidines kill the
parasites by acting on the nervous receptors causing a spastic paralysis.
All three classes of compound have excellent efficacy against the adult parasites, but
since each dewormer class has a defined mode of action with a different level of activity
against various developing and encysted larvae. The time it takes for larvae missed by
treatment to develop into an adult parasite following treatment depends upon what larval
stage the product is efficacious against. It takes longer for late L3 larvae to develop into
an adult parasite than it will for late L4 larva. This difference can be measured in the time
it takes for worm eggs to reappear in the feces following treatment. The longer it takes
for eggs to reappear the more effective the product is against both the developing and
encysted larvae.
Using products correctly and understanding their characteristics can help keep all classes
of products viable. Fenbendazole, for example, is an excellent product when used in a
strategic deworming schedule. However, if parasite contamination is allowed to develop
in the environment and parasite levels increases in the animals until a high population of
encysted larvae are present in high numbers, the efficacy of fenbendazole at the
recommended dose is drastically reduced.
Two key issues have been identified with fenbendazole that can affect its efficacy. The first issue is that this compound is not very soluble in liquids such as gastric juices or blood. The second issue is that it kills the parasite by destroying it’s ability to metabolize food. Encysted larvae are in an arrested state with reduced metabolism and reduced absorption of nutrients. Because of fenbendazole’s low solubility and reduced metabolism of the encysted larvae, the product needs direct physical contact to kill these encysted parasites. When fenbendazole is given at 10 times the recommended dose spread over a five-day period it is successful against both developing and encysted larvae (10 mg/kg given daily for five days). By flooding the gastrointestinal tract with molecules of fenbendazole, direct contact is made with the encysted larvae successfully killing them.
IX. Fecal Monitoring for Parasite Eggs is the Best Way to Determine
Whether a Deworming Program is Effective:
The Modified Wisconsin Sugar Flotation Technique is a quantitative fecal exam that is conducted by floating worm eggs out of concentrated fecal material so they can be found and identified under a microscope. The fecal exam is a simple and effective way to check whether an
animal is infected with gastro-intestinal parasites. Fecal worm egg counts, if conducted correctly, can also determine the general type of parasites present such as: pinworms, threadworms, roundworms (Parascaris), strongyles and tapeworms. The Modified Wisconsin Sugar Flotation Method is highly sensitive for use with horses (.3 egg/1 gram sample) such that negative counts indicate the absence of adult parasites. Repeated negative counts indicate a parasite-free status. Fecal worm egg count can also provide accurate information on total numbers of worm eggs shed per pound of feces which determines the rate by which an animal is re-contaminating its environment.
B. The best way to determine whether a dewormer is effective is to conduct a fecal worm egg reduction test (FECRT). This test is accomplished by conducting a fecal exam before treatment and again 10-14 days following treatment with a dewormer. Percent reduction in fecal worm egg counts due to treatment is calculated by subtracting the post-treatment egg count from the pre-treatment egg count divided by the pretreatment egg count. If the percent reduction is not 90% or greater, “parasite-resistance” is a possibility and the animals in question should be monitored regularly until negative counts are achieved. Conducting a single fecal exam  following treatment is also effective but knowing the level of egg shedding prior to treatment helps determine percentage reduction following treatment.
C. Taking Fecal worm egg counts should be an important part of the standard procedure for all equine operations. Monitoring fecals should be conducted at least semi-annually to monitor treatment progress. Fecal checks can be run any time of the year, however, one of the best time to sample horses is during the winter months to make sure the animals are parasite-free
when environmental contamination is at its lowest point and to make sure the animals are
not re-contaminating their environment immediately when grazing returns in the spring.
Another good time to take fecals is in late summer or early fall in order to monitor
whether the annual treatment program is reducing larval build-up on the pastures and
subsequent worm build-up in the animals.
The Modified Wisconsin Sugar Fecal Technique: A 3-gram fecal sample is mixed with a saturated sugar solution designed to float the eggs out of the fecal matter. The samples are strained to remove large debris, then pour into a 15 ml taper test tube and centrifuged at a low RPM (<1000) for five minutes which increases the egg recover rate by a significant amount. After centrifuging, a few drops of sugar are added to form a meniscus on top of the tube. A cover slip is placed on the top of the tube for two minutes, removes and examined under the  microscope at 40X magnification. Eggs are identified to type and counted.
The collection process is conducted using a sealable bag or baggie, invert the bag like a
glove and pick-up freshly dropped fecal material the size of a golf ball from each horse to
check for parasites. Keep each individual sample separate. Seal each bag and write on the
bag to identify the horse and date of collection. Keep samples cool after collection since
heat causes the eggs hatch and freezing distorts the eggs. For best results:
1. Refrigerate before shipping, then ship with a freezer pack or frozen water bottle.
2. Payment: Include a check for $5 for each sample sent.
3. Don’t forget to include return address/fax number or e-mail address for returning
sample results.
Ship to: MidAmerica Ag Research
3705 Sequoia Trail
Verona, WI 53593
Ph: 608-798-4901