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Conflicting information about worm control

For sheep and goat producers, especially inexperienced ones, knowing how to control internal parasites (worms) in their flocks and herds can be frustrating, as conflicting information is given by practicing veterinarians, veterinary pathologists, animal scientists, extension agents, producers, pharmaceutical companies, feed stores, fact sheets, and internet articles.

Who's right? Who's wrong? Who do you listen to? What do you do?

Gastro-intestinal parasites (also called worms, stomach worms, roundworms, nematodes, and strongyles) are the most significant health problem affecting sheep and goats.

They cost producers millions of dollars each year in production losses, treatment costs, and death losses.

Sheep and goats are affected mostly by the strongyle (meaning round) family of worms. In warm, moist climates, the barber pole worm (Haemonchus contortus) is the primary parasite affecting small ruminants.

Coccidia, a protozoa parasite, can also cause significant losses, especially in newly weaned kids and lambs.


Where to get information

Your local vet
I mean no offense to the veterinary profession when I say that many veterinarians lack the knowledge and/or training to properly advise sheep and goat producers on internal parasite control. In fact, veterinarians are sometimes guilty of dispensing out-dated recommendations, such as frequent deworming and rotation of anthelmintics.


Some continue to advocate the use of injectable dewormers, which hastens the development of drug-resistant worms. I'm not certain that some vets appreciate the level of anthelmintic resistance that exists on U.S. sheep and goats farms. Few veterinary clinics perform fecal egg counts or the fecal egg count reduction test (to determine drug efficacy).

I would imagine that the undergraduate and veterinary education of many veterinarians included very little information about small ruminants. I have two animal science degrees and can't recall ever studying anything about goats.

Many veterinarians lack an incentive (financial or otherwise) to seek continuing education on small ruminants (if it's even available), let alone learn the specifics of controlling parasites in these minor species.

The situation may be gradually improving. The continued growth of the goat industry and the popularity of camelid ownership is necessitating the need for more small ruminant veterinary expertise. At the same time, producers need to meet the veterinary profession halfway by including their veterinarian in their herd health program, not just calling them when an animal is on death's door and expecting them to perform a miracle.

By including veterinarians in their herd health programs, sheep and goat producers can enhance the small ruminant expertise of the veterinary profession.The veterinary-client relationship has to be financially beneficial for both parties.

One way to bridge the financial gap is to bring the affected animal to the vet office. Most sheep and goats can be easily transported. Other situations call for a farm visit and consultation by the vet. Producers need to always remember that extra-label drug use requires a veterinary prescription and a valid veterinarian-patient-client relationship.

State diagnostic labs

It is always a good idea to have a necropsy performed on an animal that dies unexpectedly or when you are losing several animals to unknown causes. Some states perform necropsies for free, while others charge a fee. Some practicing veterinarians will perform autopsies. Worms will be found in most small ruminants, so it is the severity of infection that is more important than the presense of worms in the gut.

You should give a detailed history of the animal to be necroposied, including symptoms and treatments. Tell the veterinary pathologist what you think the animal died from (if you have any ideas). If the pathologist knows what to look for, he/she is likely to get a more accurate diagnosis.

At the same time, don't be afraid to ask the pathologist questions or challenge the diagnosis. Almost every sheep and goat I have ever taken to a diagnostic lab was said to have died of worms or pneumonia. While some may have, these are common conditions seen in the animal post-mortem, but they are not always the cause of death, especially when the animal's clinical symptoms and treatment history are inconsistent with these diagnoses. An accurate diagnosis can not usually be made unless the history and clinical symptoms of the animal are considered.

Your county agent (educator)
In the United States, there is an extension office in every county or region. The purpose of Extension is to link university research with producers. Many other countries have similar services for their farmers. I would encourage all sheep and goat producers to get acquainted with their local county (agricultural) extension agent. Sometimes, it is the 4-H agent who has knowledge about livestock.


If there is not an extension agent in your county who is knowledgeable about livestock, there may be a regional livestock specialist who is assigned to your county. Finding knowledge specific to small ruminants can be more difficult, and there may be only one or two extension agents in your state who have specific knowledge. If you're close to another county or state, you can slip across the line to get your information. It is usually the Extension Services that provide training in the FAMACHA© system. If you require training, this is who you should ask.

Web sites
There are many web sites and articles on the internet that address internal parasite control in small ruminants. They, too, offer conflicting information and many advocate out-dated recommendations. Always check the date of the publication you are reading. Practices that were recommended previously may no longer be advisable, due to the changes that have occurred. Peer-reviewed university fact sheets usually contain more reliable information than those written by lay people. Commercial companies offer valuable information, but keep in mind that they usually have a product to sell.


It's best to read the results of research trials or fact sheets that compile research results. Some of best parasite work is done outside of the United States, so be sure to glean research abstracts from Europe, New Zealand, Canada, Australia, and South Africa. There are many different scientific journals in which parasite trials involving small ruminants are published. At the same time, some research is flawed. While it may be hard for the lay person to evaluate the quality of research, don't accept all research as the "gospel."

The ability to evaluate information is increasingly important in today's time of rapid news dissemniation. Just because someone took the time to put it on the Internet doesn't mean the information is reliable. Apply logic to everything you read or hear. Ask yourself if the information makes sense? What is the bias of the information provider? Is he/she trying to sell you something? Look for a scientific basis to the information?

Recently, a company that sells garlic juice (for parasite control in livestock) asked me to put a link to their company on my web site. I asked them to provide a scientific basis for their product? I haven't heard from them. I'm all in favor of "natural" anthelmintics, but only if they work. We need controlled studies to evaluate the efficacy of any treatment before it can be recomended to producers.

Understanding the biology and life cycle of the parasites can help you apply the logic argument to the information you receive. It's also important to understand host resistance and behavior and how environmental conditions affect parasitism. We know that young stock and females that have just lambed or kidded are more susceptible to the effects of internal parasites; therefore, it's logical to focus our efforts and resources on them, while not totally ignoring the rest of our animals. It's logical that Boer goats are more susceptible to worms, as they developed in a hot, dry climate.

Do your own research
There are numerous programs (e.g. SARE) that offer grant funds to farmers to do on-farm research. It's possible for any producer to test his/her hypothesis of what will control internal parasites on his/her farm. Most granting agencies will require the involvement of a county agent agent or similar person. Be sure to have a control group, so that you can be certain that the changes you observe are due to your treatment. For example, if you wanted to evaluate the efficacy of a natural dewormer, you would deworm half of the group of animals and leave the other half untreated. Data would be collected from both groups, and both groups would need to be managed the same.


Demand research
Each state has one or two land grant universities. Land grant universities are publically funded. The scientists and extension specialists and agents work for you: the public, the tax paper. If they're not doing what you need, demand it. Most researchers and extension people value the input of producers and are committed to serving the needs of their local community and state. If the research you want done can't be done with university facilities and animals, offer your farm and herd for an on-farm studies. The results from on-farm studies are often more practical than the results from university studies, as universities don't face the same constraints as farms and individual producers.


Who are the experts?
Some veterinarians, parasitologists, researchers, and extension educators specialize in small ruminant parasite control. The American Consortium for Small Ruminant Parasite Control (ACSRPC) is a group of such people. They meet twice a year to discuss parasite control and compare research data. They collaborate on research and extension programs. This is the group that was responsible for bringing the FAMACHA© system to the United States and validating it for sheep and goats in the U.S. The consortium has a web site in which they share the results of their research.

WormBoss is an Australian program which combines their nation's knowledge on sheep worms and their management. Their web site contains a wealth of information pertaining to internal parasite control.  PARASOL (Parasite Solutions) is a European framework with 17 partners from 10 countries. Their specific objective is "safer and environmentally friendly production methods and technologies and healthier foodstuffs, methods for the control of helminths in livestock." South African researchers developed the FAMACHA© system for managing haemonchosis in sheep and goats.


What are the important issues pertaining to parasite control?

Resistance to anthelmintics
The overriding issue that is driving internal parasite control in the 21st century is anthelmintic resistance. Though the extent and severity varies by geographic region and individual farms, parasitic worms have become resistant to anthelmintics in all three drug classes (benzimidazoles, nicotinics, and macrolytic lactones). As a result, worm control strategies must not only control disease and prevent death loss in sheep and goats, they must minimize the continued development of resistant worms.

In the past, it was commonplace to deworm sheep and goats on a regular basis with little regard for the need of the individual animal. Anthelmintics were "cheap," they worked, and even if the animals weren't parasitized, we figured performance would be enhanced if the animal was ridded of its parasites. It was commonplace to treat every animal each time we dewormed. Never mind that if only treated animals were moved to a clean pasture, as was the recommendation, the only worms on that pasture would be resistant worms.

We constantly rotated anthelmintics or we didn't rotate them at all. Frequent exposure to the anthelmintics enabled the worms to develop resistance genes. Each time an animal is dewormed, the only worms that survive are those that are resistant to treatment. These worms breed with each other and the next generation, too, cannot be killed by the anthelmintic.

Anthelmintic resistance was hastened every time we put the drug in the animal's mouth instead of down its throat, injected an anthelminic, or poured it on the animal's back. Underdosing leads to more rapid development of drug-resistant worms. Most producers would set their drenching equipment for the average animal in the group.

We might have quarantined new animals, but likely did not deworm them with multiple dewormers to prevent the introduction of drug-resistant worms. Australian researchers recently identified different strains of the barber pole worm. So now, not only does a farm need to prevent introduction of drug-resistant worms, but also the introduction of more virulent strains of worms. These practices caught up with us. If these practics continue, eventually no anthelmintic will be able to kill a parasite and we'll wind up with a bunch of dead sheep and goats.


To have an effective parasite control program on your farm, you need to know what anthelmintics still work. Producers

who fail to evaluate the efficacy of anthelmintics on their farms are essentially shooting in the dark because they do not know if the drug they give to a sick animal is going to be effective. There are two ways to test for drug-resistance: the fecal egg count reduction test (FECRT) and the DrenchRite© (larval development assay, LDA).


With the FECRT, fecal samples are analyzed before and 7 to 14 days after anthelmintic treatment. Resistance is noted if the treatment fails to reduce the egg count by 95 percent or more. Severe resistance is noted when the egg count is reduced by 60 percent or less. The FECRT test needs to be repeated for each drug. Half of the test subjects should be left untreated, so that the changes in egg counts can be attributed to the treatment and not something else.

With the DrenchRite© test, a pooled fecal sample is collected from a group of animals (preferably from those with the poorest FAMACHA© scores). After the egg count is determined, the eggs are allowed to hatch into larvae. Drug resistance is determined by exposing the larvae to the different anthelmintics. Resistance to all the anthelmintics can be determined with one pooled fecal sample and resistance can be differentiated for different species of stomach worms.

Sustainable production practices
The public is demanding more sustainable production practices to protect the environment and the safety of the food supply. While anthelmintics may be perfectly safe to use (when labeled directions are followed), the public would prefer that crops and livestock be raised with fewer chemicals and pharmaceuticals, regardless. This shouldn't bother producers and make them defensive. Using less chemicals and pharmaceuticals has the potential to reduce production costs. At the same time, we can't let our animals die from worms. The pharmaceutical-only approach needs to be replaced by a more integrated or holistic worm control program which features many different management practices.

Using fewer chemicals and pharmaceuticals requires a paradigm shift for many producers. Over the years, we have been taught that chemicals and pharmaceuticals are good management practices and that they enhance the performance of the crop or animal by ridding the environment of the pest that is competing for the same nutrients. While this approach to agricultural production has paid dividends, in terms of increased production, it has not come without costs (social, environmental, and animal welfare).

While I am not a disciple of the organic or grass-fed (100%) movement, other than to extract more money out of wealthy consumers, I see the need to reduce the use of chemicals and pharmaceuticals in agricultural production by pinpointing the need for their use vs. spraying the whole field or deworming the entire flock. Crop IPM (integrated pest management) is a very successful program in which field "scouts" evaluate crop fields and report which parts of the fields should be sprayed and when.

Integrated parasite management (IPM) operates on the same principle by identifying which animals need dewormed and when. When the barber pole worm in the parasite of primary concern, the FAMACHA system can be used to determine the need for deworming individual animals. Equally important, it identifies animals that do not require anthelmintic treatment. Controlling other parasites is more complicated as their clinical signs can be caused by many other things. For example, every lamb or kid that has diarrhea is not parasitized vs. most anemic sheep and goats (or those with bottle jaw) are parasitized by the barber pole worm.

I'm not ready to throw out anthelmintics or coccidiostats. In fact, I criticize the organic standards for not allowing targetted deworming or the strategic use of coccidiostats. But I think the time has come for us to use pharmaceuticals for medical purposes and not as "performance- enhancers." If a sheep or goat needs dewormed, deworm it. If it doesn't, then don't. I think the public wants sick animals to be treated. They just don't want them being treated sub-therapeutically or needlessly, as they see it. Commercial companies are already looking for natural methods to "enhance" health and performance of livestock. Give them some time.

Worms are not the enemy
All sheep and goats have worms in their gut. It is normal. It is okay. The goal of parasite control should not be to eliminate parasites from the animal's system. There have been consequences to doing this in people. Parasites are believed to play an important role in immunity. Young animals need to be exposed to parasites in order to develop immunity. It's only when they're exposed to too many parasites or their immunity is compromised due to disease or nutrition that they become clinically parasitized and are at risk to die.

When animals become clinically parasitized, the system is out-of-balance. In the short term, you need to deworm parasitized animals, but in the long run, you need to find other ways to keep the system from getting out-of-balance. Overstocking (overgrazing) is the primary cause of parasitism in small ruminants. You'd be amazed what selling animals or putting them in dry lot will do for your parasite control program.

The only time a negative fecal test or zero egg count is desirable is when you introduce a new sheep or goat to your farm. To prevent the introduction of drug-resistant worms to your farm, your goal should be to rid the new animal of all parasites.

The Research revolution
In my opinion, the most exciting aspect of this subject is the wealth of information that is coming out. Because of the severity of internal parasitism in small ruminants and the widespread emergence of drug-resistant worms, a considerable amount of research is being conducted in sheep and goat raising areas throughout the world. We are learning so much, and viable alternatives are gradually coming to light.

Researchers have shown that a nematode-trapping fungus can disrupt the life cycle of parasites on pasture. Though it needs to be used with caution in sheep, copper oxide wire particles have been demonstrated to reduce barber pole worm infection in lambs and kids. A vaccine shows promise; the challenge is maintaining its efficacy in recombinant form. There is scientific proof that some breeds of sheep and goats are more resistant to worms than others. The same can be said of individual animals. The sheep and goat genomes have been mapped. Scientists are looking for genetic markers to identify worm resistant animals. Genetics probably offers the best long term solution for worm control in livestock.

Natural and herbal dewormers are being studied increasingly by farmers, universities, and research centers. So far, none have been consistently effective, but it is probably only a matter of time before viable alternative(s) is found. Sericea lespedeza (a warm season legume) has been shown to have "anthelmintic-like" properties as fresh forage, hay, and pellets. Though not studied as extensivley in the U.S., there numerous other forages which contain high levels of condensed tannins. In addition to containing some condensed tannins, chicory contains sesquiterpene lactones, which seem to prevent parasite growth.

Parasite control today

With all this said, what's a producer to do to control parasitism in his/her herd or flock. Unfortunately, there is no simple answer or recipe. Effective parasite control will involve a variety of management practices, including the targetted use of anthelmintics. What works on one farm may not work on another. What works one year may not work the next. Each farm, year, and animal is different. As you go down this list of recommendations, ask yourself if they make sense to you and will help control worms on your farm.

Good management and common sense

Start with sanitary conditions for your animals.

Do not feed on the ground.

Feed hay, grain, and minerals in feeders that cannot easily be contaminated with feces.

Pick up, hang up, and put feeders away (after feeding) to keep them clean.

Keep water recepticles clean. Change water frequently.

Do not overstock pens and pastures.

Do not rely on unproven natural products to control parasitism.

Evaluate ewes and does prior to lambing and kidding to determine their need for deworming.

Keep sheep and goats in drylot to keep them from becoming infected with parasites or to preventre-infection.

Proper anthelmintic use - manage drug resistance

Use the FAMACHA© system to determine which animals should be dewormed (and which should not) for barber pole worm infection.

Deworm all sheep and goats with bottlejaw, regardless of their FAMACHA© scores.

Administer all anthelmintics orally using a syringe with a long metal nozzle (Exception: use moxidectin injectable in goats).

Do not inject or pour anthelmintics on a sheep or goat's back.

Weigh animals to determine proper dosage of anthelmintics. Do not underdose.

Give goats higher dosages of anthelmintics (typically 2x the sheep or cattle dose; exception: 1.5x dose of levamisole)

Fast sheep and goats prior to administration of benzimidazole drugs and ivermectin.

Do not move sheep and goats that have all been dewormed to a clean pasture.

Don't overuse (or misuse) moxidectin or levamisole as these anthelmintics tend to be the most effective on most farms.

Quarantine and deworm new sheep and goats with anthelmintics from two different chemical classes to prevent the introduction of anthelmintic-resistant worms.

Seek veterinary approval and advice for extra-label use of anthelmintics.

Fecal testing

Use the fecal egg count reduction test or laraval development assay (LDA, DrenchRite®) to determine drug efficacy.

Learn to do your own fecal egg counts. You can buy a green-lined McMaster slide from

Use fecal egg counts to monitor pasture contamination.

Use fecal egg counts to determine genetic differences in your livestock.

Do not use fecal testing (alone) to determine the need to deworm an animal.

Use the fecal egg count reduction test to determine the efficacy of alternative treatments.


Maintain sheep and goats on a moderate to high plane of nutrition.

Provide supplemental nutrition when pasture conditions are poor due to a seasonal pasture slump or drought conditions.

Provide supplemental protein on pasture to reduce egg counts in lambs and kids.

Increased protein in the ration during late gestation to reduce the periparturient rise in worm eggs.

Incorporate tannin-rich forages (e.g. sericea lespedeza) into the grazing program.

Use body condition scoring (on a regular basis) to evaluate your nutritional program and determine the need for changes.


Favor resistant breeds of sheep and goats in your breeding program.

Cull sheep and goats that require frequent deworming or have consistently high worm egg counts.

Select rams and bucks with low fecal egg counts.

Pasture and grazing management

Implement rotational grazing practices to prevent sheep and goats from grazing severly infected pastures.

Rest pastures to reduce parasite infection level and give plants time to regrow.

Create clean pastures by removing a hay crop from the pasture field.

Do not allow livestock to graze forage below 2 inches; ideally four inches.

Graze taller forages.

Allow livestock, especially goats, to browse.

Co-graze sheep and/or goats with cattle and/or horses to reduce the parasite load on the pastures and ingestion of infective larvae.

Reduce the ingestion of infective worm larvae by delaying grazing until after the dew is lifted.

This article was written in 2008 by Susan Schoenian.

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