The Barber Pole Worm in Sheep and Goats
By Jeanne Breneman
Stomach and intestinal worms are the single biggest health problem for small ruminant (goat and sheep) owners. Of the stomach and intestinal worms, the Barber Pole Worm (Haemonchus contortis) is considered the worst of the worst. Fortunately, controlling the barber pole worm largely controls the other stomach and intestinal worm species at the same time. Examples of other stomach and intestinal worms include brown stomach worms (Teladorsagia circumcincta and Ostertagia trifurcate), and the stomach hair worm (Trichostrongylus axei).
Because Haemonchus lives in the abomasum (fourth stomach) and feeds on blood, the primary health concern is anemia and the serious (even deadly) effects of that. One visible symptom of severe anemia is bottle jaw, an edema (accumulation of fluid) under the animal’s jaw. Haemonchus does not typically cause scours (diarrhea).
Testing for anemia and performing fecal egg counts are two methods of monitoring the problem in your sheep and goats. Besides monitoring, we also recommend using a combination of thoughtful control strategies appropriate for your situation to deter the parasite. Use of anthelmintic (dewormer) drugs is only one of these strategies, and it should be used in a judicious and targeted way so as not to contribute to parasite resistance on your property.
In this article, we will examine the barber pole worm specifically, with a focus on the current best practices for control. For a broader discussion of diseases and parasites affecting sheep and goats, see our blog article, Common Small Ruminant Diseases and Parasites.
The Problem of Parasite Resistance to Anthelmintic Drugs
Over time, Haemonchus (and other parasites too) have become increasingly resistant to the three groups of anthelmintic drugs that are available. Generally, worms that develop resistance to one drug can no longer be killed by any member of the group to which that drug belongs. While rotating between drug groups used to be effective, the worms are now developing resistance to all three groups.
Worm populations develop resistance to drugs primarily by a process of natural selection. The ones with genetic resistance survive and multiply, passing resistance on to their offspring. When you use an anthelmintic drug to which some worms have developed resistance, you give the resistant worms (and their offspring) a survival advantage.
The development of resistance to anthelmintic drugs is a natural process, but it can be slowed. Many farm practices inadvertently speed up the process. For example, deworming all animals at once greatly increases the percentage of worms that are resistant as those are the ones that survive the blanket deworming. Another example is moving animals to a “clean” pasture after deworming, because the resistant worms go with them and make up a large percentage of the total worm population in the new pasture. Underdosing with anthelmintics is another potential problem because what doesn’t kill you (if you’re a parasite), makes you stronger!
“Refugia” is an important concept in any discussion of parasite resistance. Refugia is the population of worms that have not been exposed to anthelmintic drugs and are less likely to be resistant. Refugia is a good thing because it dilutes the population of resistant worms and has the effect of slowing down the development of total resistance in a worm population.
In selecting parasite control strategies, it is a good idea to avoid practices that kill off the refugia. Killing off the refugia skews the ratio of resistant to non-resistant worms in favor of the resistant worms. The larger the percentage of non-resistant worms, the more time it will take for genetic resistance to become the norm.
Integrated Parasite Management combines selective administration of anthelmintic drugs with thoughtful farm practices to:
- Attack the problem of worm infestation on multiple levels.
- Slow the tendency of worms to develop resistance to drugs.
We will talk more about Integrated Parasite Management shortly.
A Look at the Worm Itself
At about an inch long, adult Haemonchus worms are visible to the naked eye. There are both male and female worms. The common name, “barber pole worm”, comes from the barber pole effect created by the worm’s physiology – the white reproductive system is entwined with the red (from the host’s blood) intestine. The worm has a “tooth” at one end that nicks the surface of the abomasum, so the worm can consume the resulting blood.
Understanding the life cycle of the worm is useful when deciding which integrated parasite management strategies to utilize on your property. The goal, of course, is to interrupt the life cycle. The female worm lays eggs in the abomasum. The eggs are passed to the external environment in the host’s manure. The eggs hatch in the manure, feed on bacteria, and the larvae molt a couple of times as they grow. The third stage larva is the infective stage. Infective larvae live on grass, within a few inches of the ground. The sheep and goats ingest the larvae while grazing and become infected.
How long it takes from egg to third stage larva is temperature-dependent, ranging from several days to weeks or even months. But within three weeks after ingestion, the worms have matured and are laying eggs to start the cycle again. An individual worm typically lives a few months.
In the external environment, the eggs and larvae do not survive well in freezing temperatures. But larvae do have the ability to lay dormant (and undetectable) inside the host until warmer weather when they mature to adulthood. In California, cold is less of a problem for the parasite than the risk of desiccation in the dry heat of summer. Worms are most prevalent at times when the conditions outside the host (temperature and moisture) are conducive to egg hatching and early larval growth. Warm, moist conditions are ideal. In California, that means areas with natural water or irrigation have a bigger potential problem.
Integrated Parasite Management
Integrated Parasite Management (IPM) is an alternative to relying exclusively on anthelmintic drugs to control parasites, thereby slowing the development of parasite resistance to drugs. By “management”, we mean keeping the level of parasite infestation below the threshold that causes disease. All small ruminants that graze on grass have worms, so parasite eradication is not really feasible, and is not the goal.
By “integrated”, we mean employing multiple strategies simultaneously, and limiting the use of anthelmintic drugs to those individual animals that need it most.
Different sheep and goat owners employ different combinations of strategies to achieve IPM, including some strategies in the areas of pasture management, manure management, maximizing the natural immunity of the host animals, and selective use of anthelmintic drugs.
You can manage your pasture(s) in a variety of ways, depending on your situation. Here are some examples:
- Reduce animal density on pastures.
- Alternate grazing between species or combine multiple species for simultaneous grazing. Most parasites are specific to a host animal species, so for example, cattle would simply digest goat parasites.
- Rotate pastures between grazing and harvesting for hay.
- Let pastures grow long before grazing. Larvae typically stay within six inches of the ground, so taking the animals off the pasture before the grass gets shorter than that reduces the number of worms they ingest. Rotating animals among sections of pasture allows you to keep all sections on the long side.
- Promote browsing (heads up) versus grazing (heads down). Sheep mainly graze. Goats will browse taller, non-grass foliage where there are no worms.
- You could avoid pasture altogether and keep your animals on dry lots or in barns. No grass means limited opportunity to ingest worms. Whenever you feed your animals, as opposed to letting them graze, it’s a good idea to feed them from a raised surface or a container since the parasites reside on or near the ground.
Manure management strategies are more practical in some setups than in others. They include:
- Keeping poultry on the property to pick apart manure, allowing eggs and larvae to dry out and die.
- If you have the equipment to do so, drag pastures to break up manure. This is another way to expose the eggs and larvae to sun and air, drying them out. Keep the life cycle of the worm in mind and establish a dragging schedule that prevents the larvae from reaching the infective third stage.
- In smaller setups, you could collect the manure and dispose of it rather than leaving it on the land.
Leverage the Natural Immunity of Host Animals to the Parasite
Sheep and goats (sheep more than goats) can develop some immunity to GI worms. Immunity does not mean the parasites die in the host. Rather, it means the host can accommodate the parasites without being weakened by them. Immunity comes with maturity only. Young animals will always be more vulnerable.
To use immunity to your advantage, keep the most vulnerable animals on the safest pastures. Vulnerable animals include:
- Lambs and kids.
- Lactating does and ewes.
- Animals showing signs of stress for whatever reason.
Immunity seems to be genetic, and some individual animals develop more genetic immunity than others. You can gauge the immunity of an individual animal by performing a fecal egg count to see how much parasite load there is, and then recording a FAMACHA score (anemia test) to see how the parasites are (or are not) affecting the animal. You will see that some animals can have a higher parasite load without suffering any anemia. You can then take this into consideration in your breeding program. We’ll give you more information on FAMACHA scoring shortly.
Some breeds tend to have greater genetic immunity to parasites than others. More information is available for sheep than for goats in this regard.
Nutrition is a big factor in maximizing the natural immunity of all your animals. Be sure the diet you provide has sufficient protein, and good quality vitamins and minerals.
Selective Use of Anthelmintic Drugs
We include the use of anthelmintic drugs last in the list of IPM strategies to emphasize again that this should be used selectively to slow the development of parasite resistance.
Typically, 30% of the animals have 80% of the worms (or eggs). By identifying the individuals that most need to be dewormed, and deworming only those animals, you contribute less to the development of parasite resistance. It is a nice bonus that this also saves you time and money!
For the barber pole worm only, FAMACHA scoring is the best way to determine which individuals need deworming, based on the degree of anemia the worms are causing. FAMACHA scoring measures anemia using eye membrane color. It is a simple, non-invasive test that anyone can learn to perform. For other GI parasites, fecal egg counts can be useful. Fecal egg counts do not map to the effect on the animal the way FAMACHA scoring does, however. Remember that some animals have more natural immunity than others and can tolerate a higher parasite load. For selective breeding to increase host immunity to parasites, a combination of FAMACHA scoring and fecal egg counts is highly effective. We recommend that you keep good records so you can track changes in each animal.
Sheep and goats metabolize drugs differently. It is a good idea to partner with your veterinarian to select the anthelmintic drug, determine accurate dosing, and provide guidance on maximizing the absorption of the drug. Use of most anthelmintic drugs for goats and sheep is considered off-label, so dosing guidance is not provided by the manufacturer. You will need to know each animal’s weight because dosing is based on weight. Remember that underdosing contributes to development of parasite resistance.
If you are raising animals for food, be sure to take withdrawal time into consideration. In other words, allow enough time after administration of the drug, before slaughter, for the meat to be safe to eat. Consult your veterinarian if you are not sure about the withdrawal time for the drug you are using. Administer anthelmintic drugs only by mouth as opposed to injection to avoid scarring of the meat.
FAMACHA scoring is a way to check for the anemia that Haemonchus infestation causes. The idea is to treat animals selectively based on the results of this test.
FAMACHA stands for FAffa MAlan CHArt, named for one of the developers, Dr. Francois “Faffa” Malan. Dr. Malan and his team developed this test in South Africa in response to severe parasite resistance to anthelmintic drugs. It has since become widely used in many parts of the world and was introduced into the U.S. in 2003 by the American Consortium for Small Ruminant Parasite Control (ACSRPC). You might be wondering if this test distinguishes between barber pole worm anemia and other possible causes of anemia—the answer is no, it does not. However, barber pole worm is by far the most likely cause.
With FAMACHA, you use a “cover, push, pull, pop” technique to expose the inner eye membrane of the sheep or goat. You then compare the color of the membrane to the FAMACHA color chart and record the result (the score) as a number. It is important to learn how to perform the technique properly because just pulling the lower eyelid down might not give an accurate result. Once you know the score for each animal, you can deworm just those animals with scores of 4 and 5, and maybe 3.
Tip: It is recommended to perform the test in the sun for best visibility.
You can get trained and certified to do FAMACHA scoring by completing an online course and hands-on training. Certification gives you access to FAMACHA color charts. Your veterinarian can also do FAMACHA scoring for you or confirm your results until you have confidence in your own assessments.
The ACSRPC’s website is an excellent online resource for FAMACHA certification and other small ruminant parasite information: https://www.wormx.info/.
The University of Rhode Island offers some very helpful videos about FAMACHA scoring, Integrated Parasite Control, and performing fecal egg counts: https://web.uri.edu/sheepngoat/video/.