No matter what social media goat group you belong to or follow, eventually this question will pop up – “Which dewormer is best?” It will be followed by a plethora of answers, folks eager to share what works for their herd. So, what’s the correct answer?
The short and sweet answer: It depends!
Parasite management is multi-faceted. What works on one farm may not work at all on the next. By learning more about dewormers, parasites, and the most current recommended management practices, you can develop a program that works for YOUR farm, and you can find your “best” dewormer. For the sake of this piece, only synthetic dewormers be discussed, not herbals.
No matter what dewormer you choose, you must take care to dose appropriately. It is essential to get a good estimate or an exact weight on your animals and to know the current recommended dosage. This is an excellent reference - https://www.wormx.info/_files/ugd/6ef604_645435f117f6433594c69693a294cf59.pdf
Dewormer Classes
First, it is important to understand dewormers are divided into chemical classes. There are three major chemical classes of dewormers used in goats: benzimidazoles, imidazothiazoles, and macrocyclic lactones (1).
Benzimidazoles are the oldest dewormers and work by binding a protein necessary for cell function so the parasite basically starves. Common dewormers in this class are fenbedazoles such as Safeguard® and albendazoles such as Valbazen.® Since these dewormers have been in use the longest, you are most likely to encounter parasite resistance in this class (2).
Imidazothiazoles are few, and the only one a goat owner is likely to deal with is the levamisole Prohibit®. This class works quickly and effectively on nematodes by disrupting their nervous system (11).
Macrocyclic lactones are broken into two categories: avermectins and milbemycins. Macrocyclic lactones are effective against both internal and external parasites, though the efficacy will differ depending on the specific drug and by administration e.g. topical for external parasites like biting lice and orally for stomach worms. As to how this class works: “…it blocks the transmission of neuronal signals of the parasites, which are either paralyzed and expelled out of the body, or they starve” (12). This class is the most frequently used in small ruminants and livestock in general. Examples of avermectins include ivermectins, doramectrins, and eprinomectin. Moxidectin, most commonly used as Quest® or Cydectin®, is a milbemycin (3). A few other classes that goat owners might deal with: tetrahydropyrimidines like Morantel Tartrate® and Pyrantel® (13). Mortantel tartrates are most likely to be found in medicated feed or in pellet form. Another is the benzenesulphonamide Clorsulon, often found with another chemical such as ivermectin and called “Plus” such as Ivomec® Plus. Clorsulon is a narrow-spectrum antiparasitic, effective only against liver flukes. Finally, the isoquinoline praziquantel might be used in goats against tapeworms. It must be noted that many of these aforementioned dewormers are used off-label or extra-label in goats in the United States and off-label or extra-label use should be discussed with a veterinarian.
Choosing a Dewormer
Type of Parasite
It is a common trend on groups for folks to recommend a fecal to find out what sort of internal parasites the goat is harboring before choosing a dewormer. Fecals are never a bad idea but very specific egg identification simply to choose the correct dewormer is often unnecessary for a few reasons. Most dewormers are broad spectrum, meaning they will work on many different kinds of worms. Furthermore, it can be incredibly hard, especially for laymen, to differentiate between some species of internal parasites, especially various species of roundworms, without measuring or even hatching out the eggs. Take the graphic below for example. (If anyone knows the original source of this graphic, pleas share!)
Lungworms, liver flukes, and tapeworms are often exceptions to “broad spectrum” effectiveness. A fecal or careful observations can be helpful to identify these parasites so you can treat accordingly. You’re more likely to see tapeworm segments or proglottids (the rice-like egg-filled sacs) in fecal material than see the triangle-shaped eggs on a microscope slide. More on the most effective tapeworm treatments here. Some species of liver flukes will require a sedimentation test rather than a fecal float and lay few eggs. One species (lancet liver flukes) lay eggs that are similar in both appearance and size (smaller but this is hard to tell unless they’re side by side) to barber pole worm eggs and can be seen on a fecal float. More on the various liver flukes in an upcoming installment! Like barber pole worms, liver flukes can cause general ill thrift and anemia, even bottle jaw anemia. Most dewormers will NOT treat flukes, so it is helpful to attempt to diagnose them in order to choose an effective treatment, which typically involves either Valbazen® or a dewormer that also contains clorsulon. Additionally, the treatment must be repeated in about three weeks to catch the newly-matured flukes. Sometimes multiple treatments are warranted (8) While common dewormers do treat lungworm, these parasites can be encysted so that a specific protocol is warranted. With lungworms, a fecal float or the Baermann method is useful but it will show larvae, not eggs (15). Please note that a fecal to deny or confirm the presence of coccidia by identifying the oocysts (eggs) is helpful since you will need to use a coccidiostat rather than a dewormer. While they ARE an internal parasite, they will not be discussed in this piece because coccidia are a protozoan and cannot effectively be treated with a dewormer.
Classes and Combos
Once upon a time, it was recommended to rotate classes to improve efficacy and slow resistance. Time and more research proved this to be a recipe for resistance instead of slowing it! Later, it was recommended to use a dewormer from a single class until it was no longer effective before either increasing the dosage or choosing a dewormer from a more effective class. (9)
Today, it is recommended to use a combination treatment.
A dewormer combo consists of at least two dewormers from at least two different classes that are administered at the same time but not in the same syringe. Current research shows killing the parasites by two different methods like this improves efficacy and slows resistance to each of the chemicals used (16). For instance, a producer might use an ivermectin and a fenbendazole. A great explanation is here - https://www.wormx.info/combinations
COWPs (copper oxide wire particles) can also be used in conjunction with dewormers to improve efficacy (17).
With the exception of lungworms or liver flukes, it is recommended to dose the animal ONE time and the run another fecal in 10-14 days to make sure the treatment works. You do not have to deworm then deworm again in 10-14 days because dewormers ARE generally effective on immature parasites.
Determining Efficacy
The most accurate way to determine efficacy is a fecal egg count reduction test done on several animals, either at home or with the help of your vet. At one time, it was possible to utilize a DrenchRite® test done at the University of Georgia (20). Owners sent in fecal samples from at least 10 different animals and the lab grew out the parasites then tested their resistance to various dewormers. This test is the most accurate method of determining parasite resistance and dewormer efficacy but is currently (as of May 2022) no longer available in the United States. (I am leaving this information here in case another doctor and/or lab resume testing – my understanding is the necessary assay plates must be imported and can be difficult to obtain and the professors running these tests at the University have retired.)
A fecal egg count reduction test consists of running a fecal prior to treatment, counting the eggs on a McMaster slide, running a second fecal 10-14 days post treatment, and calculating the efficacy in the form of a percentage. It is best done on at least 6 animals but 10-15 is recommended for a more complete picture of dewormer efficacy on your farm (8). For example, let’s say you calculated an eggs per gram count of 1400 on Doe 1 before treatment. After treatment, the count was 350epg. Subtract the second fecal egg count from the first so 1400 – 350 = 1050. Divide that number by the original epg: 1400 / 1050 = .75. Multiply that by 100 to get a fecal egg count reduction percentage of 75%. In terms of parasite resistance and dewormer efficacy, a 75% kill rate is considered only marginally effective. Effective is considered anything over 95%. (18). To get a more complete picture, as mentioned, it is best to run this test on several animals then get averages. This is a time-consuming task but not difficult. Without running fecals, dewormer efficacy can be difficult to determine. Evaluating the FAMACHA score is the best way to determine if the dewormer has been effective against anemia-causing parasites. A quick note – not all parasite-induced anemia is caused by direct blood-sucking such as in the case of the barber pole worm. Take the brown stomach worm, for example. It causes damage to the abomasum which starts a chain reaction that also includes “Incomplete protein digestion decreases albumin absorption to blood” that can result in submandibular edema aka bottle jaw though the brown stomach worm does not suck blood (22). It must be noted that it takes time for animals to rebuild red blood cells even if treatment was effective, not all anemia is caused from parasites, and every so often a goat might have a poor FAMACHA score but a perfectly normal packed cell blood count score. Producers either not running fecals or dealing with fecals showing little to no evidence of a parasite issue are often left to start determining causes of anemia from most likely to least likely, ruling out what they can get definitive answers for.
Producers not running fecals must observe other physical signs, such as body condition scoring, fecal consistency, and general health but will ultimately still be playing a guessing game. Furthermore, without running fecals, especially at the appropriate time, it can be difficult to determine if the dewormer didn’t work well on a specific animal because the dewormer is no longer effective or because the animal has a very poor natural resistance and/or resilience to parasites and has already succumbed to reinfection. In the case of lancet liver flukes, you might also deal with a case of mistaken identity – seeing eggs on the slide that are actually liver fluke eggs and not strongyles. In this case, the producer is left to either try a flukicide or send a sample to professionals for a positive ID (21). Read more about managing parasites on your pastures here: https://www.wormx.info/copy-of-management
Unfortunately, it is possible that a fecal shows a reduction or lack of eggs after treatment but the adult worms are still alive. In this study published in the Australia Veterinary Journal Volume 86 Issue 11, the use of a pour-on dewormer (given as such) showed a reduced fecal egg count in the treated group. A post-deworming post mortem for both groups (treated and untreated) showed very similar numbers of adult barber pole worms in the abomasums. The pour-on treatment had only delayed egg shedding, not killed the worms (25). This is why it is not advised to use a pour-on dewormer.
It must also be noted that Stage 4 barber pole larvae will be sucking blood before maturing into an adult stage where the females will start to lay eggs. Read more about the barber pole worm’s lifecycle here. In conclusion, even fecals are not infallible but are still incredibly useful tool for a goat producer. If a producer cannot run fecals for their herds themselves, there are places to send samples. A few labs are listed here. Another is the Veterinary Parasitology Laboratory at MidAmerica Agricultural Research. There are also smaller labs within states that can offer these services. Your local vet can typically conduct a fecal float. (On a personal note, my microscope and supplies paid for themselves VERY quickly if I had been taking the same number of samples to my vet.)
Other Considerations
Mode of Administration
Most dewormers come in more than one formulation and strength, especially those in the macrocyclic lactone class. Ivermectin, for example, can be found in .5% to 1.87% strength in drenches, injectables, pastes, and pour-ons. Currently, only the ivermectin drench is approved in goats and the others are used off-label.
The newest research shows that, for internal parasites in sheep and goats, pour-ons and injectables are less effective treatments and will lead to faster dewormer resistance (24). This is especially true of very long-lasting drugs used in cattle such as LongRange™ dewormer (23), which should be avoided. Furthermore, the carrier oils in pour-on dewormers normally applied topically to cattle but given orally to goats are abrasive to the goats’ rumens. (On a personal note, I used Cydectin pour-on on my cattle for the first time this spring. Just a few drops on my hand burned quite uncomfortably - enough to make me think there would be no way I would drench my goats with this, even if it was effective.)
Animal Class
Sometimes, you must alter your preferred product and typical deworming strategy based on the animal. Is a doe pregnant? Then Valbazen® needs to be avoided as it can cause birth defects, especially in early gestation, but Safeguard® is a safe alternative still in the same chemical class. Will the animal be slaughtered soon? Are you consuming or selling the milk? Those withdrawal times or off-label usage in food animals sometimes means you need to find an alternative “best” treatment. In a combination treatment, the withdrawal times are whatever the longest individual dewormer withdrawal time is.
Each goat owner needs to find their own BEST dewormer and practice good parasite management to keep it their best for as long as possible. Please check out the sources below!
Sources for "Which Dewormer is Best for Goats?"
1. Kaminsky R, Ducray P, Jung M, Clover R, Rufener L, Bouvier J, Weber SS, Wenger A, Wieland-Berghausen S, Goebel T, Gauvry N, Pautrat F, Skripsky T, Froelich O, Komoin-Oka C, Westlund B, Sluder A, Mäser P. A new class of anthelmintics effective against drug-resistant nematodes. Nature. 2008 Mar 13;452(7184):176-80. doi: 10.1038/nature06722. PMID: 18337814.
2. https://qa.singlecare.com/blog/anthelmintics/
3. https://www.ams.usda.gov/sites/default/files/media/Fenbendazole%20TR%202015.pdf
6. https://parasitipedia.net/index.php?option=com_content&view=article&id=2646&Itemid=2932
7. https://www.extension.purdue.edu/extmedia/as/as-573-w.pdf
8. Goat Medicine
9. https://www.wormx.info/changingdogma
10. https://www.wormx.info/fecaleggcounts
12. https://parasitipedia.net/index.php?option=com_content&view=article&id=2413&Itemid=2678
13. https://parasitipedia.net/index.php?option=com_content&view=article&id=2442&Itemid=2713
14. https://parasitipedia.net/index.php?option=com_content&view=article&id=2509&Itemid=2782
15. https://www.rvc.ac.uk/Review/Parasitology/Baermann/Principle.htm
16. https://www.wormx.info/combinations
17. https://www.wormx.info/cowpcombo
18. https://www.wormx.info/single-post/2018/10/19/Determining-Dewormer-Effectiveness
19. https://www.wormx.info/ugaupdate
21. https://www.wormx.info/improvefam
22. https://parasitipedia.net/index.php?option=com_content&view=article&id=2636&Itemid=2914
23. https://www.wormx.info/longrange
24. https://www.wormx.info/oralmox
25. https://www.academia.edu/14819276/Eprinomectin_pour_on_and_the_shedding_of_Haemonchus_contortus_eggs_in_experimentally_infected_goats