Parasite management is crucial to a healthy, happy goat. The goal is a low-enough parasite burden animal health is not compromised. While there is not a singular parasite management plan that works for every farm, there are a few practices every owner should follow that will ensure goats are dewormed correctly and prolong the efficacy of chemical dewormers. Additionally, every goat owner should be aware of parasite resistance, and strive to postpone it as long as possible. “Anthelmintic resistance is defined as a heritable genetic change in a population of worms that enables some individual worms to survive drug treatments that are generally effective against the same species and stage of infection at the same dose rate,” according to “Biology of Anthelmintic Resistance: These Ain’t Your Father’s Parasites” by Dr. Ray M. Kaplan.
First, owners need to understand there are different classes of dewormers, also referred to as anthelmintics. A class consists of dewormers that share a similar mode of action. Many dewormers are off-label – not approved for goats without a valid relationship with a veterinarian. For a handy chart on dewormers, complete with dosages and crucial notes, visit https://www.wormx.info/dewormers or search the files at Goat Vet Corner group on Facebook.
The first class is benzimidazoles, also called the “white dewormers.” Dewormers in this class include fenbendazoles, albendazoles, and oxybendazole. Since this class has been around the longest, stomach worms are often resistant to these dewormers. Remember that resistance varies from farm to farm. Fenbendazoles are effective against tapeworms and albendazoles are effective against adult liver flukes.
The second class is the macrocyclic lactones, which include avermectins and milbemycines. According to “Choosing the Right Drug for Worm Control” by Dr. Lisa Williamson – “Avermectins include ivermectin, eprinomectin, and doramectin. Moxidectin, a milbemycin, is chemically very similar to the avermectins…Moxidectin is a more potent, lipophilic macrocyclic lactone than ivermectin.” Though they are in the same class, moxidectin can still be effective where ivermectin is not.
The third class is the Imidazothiazole/tetrahydropyrimidine class. Common class members include levamisol and mortanel. Levamisol, while it is the easiest to overdose and MUST be carefully dosed by weight, is often the most effective class currently available in the United States.
|DRUG CLASS||DRUG||COMMON CLASS MEMBERS|
|Benzimidazoles||fenbendazoles, albendazoles, oxybendazoles||Safeguard, Panacur|
|Macrocyclic lactones||ivermectins, moxidectin, doramectin, eprinomectin||Ivomec, Quest, Cydectin, Dectomax, Eprinex|
|Imidazothiazole/tetrahydropyrimidine||levamisol, mortanel tartrate,||Prohibit, Rumatel|
Do NOT rotate dewormers.
Rotating between classes and dewormers leads to parasite resistance and accelerates dewormer failure. Find what dewomer works on your farm based on fecal egg count reduction tests – determine the egg count prior to deworming compared to fecal egg count 10-14 days after deworming. An effective dewormer will have at least a 95% kill rate. Dewormers can still be useful with a lower kill rate, but it might be a good idea to either combine two classes or use in conjunction with another alternative treatment, such as copper oxide wire particles or a diet high in tannins.
A DrenchRite® test is also available that determines what parasites your herd is burdened with and the effectiveness of each dewormer class on the parasites. At the time this article is written, the DrenchRite® test cost $450.
Dewormers from two or more classes can be combined to deworm new animals, or prolong the life of dewormers when resistance has been noted or a dewormer class has failed. Note that these are given at the same time, but NOT mixed together. It should be cautioned that improper use of combination dewormers could select for worms that are resistant to ALL anthelmintics. For more information on combining dewormers and the DrenchRite® test, please refer to the following: https://www.wormx.info/combinations and https://www.wormx.info/drenchriteassay.
Do NOT deworm on a schedule.
Contrary to recommendations given when dewormers first became available, deworming should not be scheduled. We now know scheduling treatment accelerates resistance, and chemical deworming should NOT be preventive. Parasite numbers wax and wane during different seasons, and in different conditions. Lactating does will likely be more susceptible to parasite burdens than a dry doe, and bucks are more likely to be susceptible in rut, etc….As detailed in the “Barber Pole Worm” article in the Winter 2017 newsletter, Barber Pole worms and other internal parasites thrive in certain conditions and will have lower survival rates in others. For example, Barber Pole worm eggs and larvae survive very well in warm, humid conditions, but use up their energy stores very quickly in dry heat. Learn about the life cycle and preferred conditions of the parasites your herd is dealing with to better manage them – Goat Biology.com has some excellent animated slides detailing the lives of common goat parasites. The American Consortium for Small Ruminant Parasite Control offers many articles and files on the subject, as well.
Deworm only the animals that require treatment.
By selecting only animals that need deworming versus deworming the entire herd, the goat-keeper does not expose all worms to the chemical, thereby slowing the worm’s ability to develop genes to resist the anthelmentic. The idea of leaving unexposed parasites is called refugia. The Latin term means “in refuge.” By leaving untreated animals and therefore unexposed worms, there will be few resistant worms to mate with many susceptible worms, and the resistant genes will be diluted in the next generation. Refugia refers both to adult worms not exposed to dewormer and the larvae and eggs on pasture that were not the product of resistant worms.
Furthermore, it is documented that the parasite burden is NOT evenly distributed among the herd. Research shows 20-30% of goats in a herd will carry up to 80% of all parasites. By first identifying, then deworming and/or culling these animals, the goat owner will greatly reduce the parasite burden both in the goats and on the pasture.
Deworm animals based on FAMACHA scores – remember this only indicates anemia that is generally caused by Barber Pole worms or liver flukes – the Five Point system, and/or a fecal showing a high eggs per gram count. Many producers misuse the FAMACHA system – check out https://www.wormx.info/dosdonts.
Fecals are crucial to determine what parasites your goats are burdened with, how heavy that burden is, and how well your dewormer and deworming practices are working. Utilize your livestock veterinarian, send in samples to the Veterinary Parasitology Laboratory (http://www.midamericaagresearch.net) or invest in your own microscope. Tolerable parasite levels will vary from farm to farm and goat to goat. Remember that some goats are more resilient to parasite burdens than others, but these animals are shedding higher numbers of eggs in the pasture.
Dose by weight to avoid under-dosing. WEIGH THE GOAT BEFORE DOSING. If you do not have access to a livestock scale, weight tapes or cloth measuring tapes are a cheap investment. Administer the dewormer correctly – from the article “Choosing the Right Drug for Worm Control” – “Delivery deep into the oral cavity avoids closure of the esophageal groove, so the medication goes into the rumen rather than the abomasum. This step facilitates longer contact time of the drug with the gastrointestinal tract and improves drug efficacy.”
Dewormers in the forms of pour-ons, injections, and long-range (persistent activity) dewormers have proved to be generally ineffective in goats. These sub-lethal levels mean many worms survive and develop those dreaded resistant genes. For further reading, check out “Should I consider using LongRange™ dewormer for parasite control in small ruminants?” by Dr. Ray Kaplan.
Fasting the animal 12-24 hours before treating with ivermectins and/or benzimadazoles is a good idea, with the exception of does in late gestation. This increases drug availability, meaning the worms will be exposed to the drug for longer and are thus more likely to be killed.
As goat producers, we are exercising parasite management, not parasite elimination.
Dr. David Fernandez explained in an online parasite information session, “No matter how hard you try, you cannot eliminate every parasite from your animals. If you try hard enough, you will create some of the toughest parasites on Earth which will eventually make your life miserable, not to mention your goats’. Instead, we need to focus on managing parasites so that they do not cause an intolerable level of harm.” In conclusion, managing – not eliminating – parasites will vary from farm to farm but ALWAYS dose correctly and treat only animals the need treated, and NEVER rotate dewormers or deworm on a schedule. Utilize tools like fecals and FAMACHA to determine which animals need treated and to determine effectiveness of the treatment.
- “Biology of Anthelmintic Resistance: These Ain’t Your Father’s Parasites”; Ray M. Kaplan, DVM, PhD, DipACVM, DipEVPC College of Veterinary Medicine University of Georgia, Athens, GA
- “Choosing the Right Drug for Worm Control”; Lisa Williamson DVM, MS, DACVIM University of Georgia College of Veterinary Medicine Athens, Georgia, USA
- “Correct Administration of Anthelmentics” Ken Pettey Department of Production Animal Studies, Gareth Bath Department of Production Animal Studies, Jan van Wyk Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria.
- “Do’s and Don’ts of FAMACHA Scoring©” Katherine Petersson, PhD Associate Professor of Animal Science, University of Rhode Island
- “Extending the Efficacy of Anthelmintics”; Lisa H Williamson, DVM, MS, DACVIM University of Georgia College of Veterinary Medicine
- “Goat and Sheep Parasite Control” (powerpoint presentation) Jerry Lamb, University of Tennessee Extension, Rhea County.
- “Refugia – Overlooked as Perhaps the Most Potent Factor Concerning the Development of Anthelmintic Resistance”  Van Wyk, J.A. (Pretoria Univ., Onderstepoort (South Africa). Veterinary Tropical Diseases Dept.)
- “Should I consider using LongRange™ dewormer for parasite control in small ruminants?”; by Dr. Ray Kaplan Professor of Parasitology, Department of Infectious Diseases College of Veterinary Medicine University of Georgia Athens, Georgia
By Kendra Shatswell
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