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November 2019 - Equine Welfare

No animal lover wants to hear or see abuse, but it’s a subject that we are often faced. Join us in November as our expert, Dr. Alina Vale answers your questions concerning equine welfare, neglect and abuse.

Click here to read this month's questions and answers.

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Internal Parasites

  1. What dewormers do you recommend during the year? How often should a fecal float be done?

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    Unfortunately, your question cannot be answered right away. There are several reasons for this. First of all, it depends on the age of the horses and what parasites they have. Different parasites require different dewormers, so you need to know what you are treating. Second, your question seems to suggest that the choice of dewormer depends on the time of year, which is not the case either. The choice of dewormer merely depends on two things; 1) what parasites the horse is harboring, and 2) what efficacy profiles these parasites exhibit to the different dewormers on the given farm. Bottom line here is that appropriate parasite testing is required to answer your question. The number of fecal tests per horse per year also depends on how old it is. For adult horses, the recommendation is two yearly fecal samples to identify the low, moderate and high strongyle shedders. Then, treatment efficacy of the chosen dewormers should be monitored as well. Once baseline efficacy has been established for each type of dewormer used, it is recommended to routinely test the efficacy at least every 2-3 years. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  2. I do fecal counts both spring and fall, routinely showing low counts. Should I deworm once a year anyway? Is it safe after not doing so in such a long time? My horse does not share pastures or paddocks with any other horse.

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    You didn’t mention how many horses you have or their age range. In a small, closed herd with only adult horses that never leave the farm, I agree that you can be pretty laid back in your parasite control efforts. However, egg counts are mainly a measure of small strongyle contamination. The AAEP guidelines recommend one or two yearly treatments to address parasites such as bloodworms, tapeworms, bots and pinworms as egg counts do not necessarily reveal their presence. A good time to treat strategically is in the fall when the grazing season is about to end. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  3. What is the most effective treatment for habronemas?

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    You are probably well aware that there are two forms of habronemiasis. The Habronema parasite is really a stomach worm, and when it follows the normal lifecycle with adult stages in the stomach and eggs in the feces, most if not all dewormers will be very effective. However, you are probably referring to the cutaneous form, where larvae are deposited by their fly vectors in wounds on the horse’s skin. This causes a chronic granulomatous dermatitis also referred to as summer sores. Many veterinarians are reporting that it has become increasingly difficult to effectively treat the larvae within these summer sores. This may have to do with the thick layer of scar tissue forming around the lesions, which makes it difficult for the dewormer to reach the larvae. But it is also very possible that there is some resistance developing to dewormers such as ivermectin. The issue is that there really aren’t any alternatives to ivermectin as it belongs to the only drug class that can be expected to effectively treat migrating parasite larvae. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  4. How often should I do fecal egg counts? I manage a boarding/lesson/show barn with 27-30 horses on the property.

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    For adult horses, a good starting point is twice a year. At least one of these two sample occasions should include a post-treatment follow-up to ensure that treatments worked as intended. Then, it is recommended to test, treat and monitor new arrivals as they have a tendency of staying elevated for a while upon arriving on a new farm. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  5. I have tried doing fecal egg counts and had cut back on use of dewormer, but my horse developed an eye infection (Uveitis) and I had to treat with Ivermectin. I feel this is a double edged sword. . . 

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    Yes, you are absolutely right that parasite control is a double-edged sword. On one hand we want to reduce further development of resistance as much as possible and on the other, our goal is to avoid parasitic disease. That said, I am not aware of any worm parasites capable of causing uveitis – certainly  not on this continent. There is an eye worm named Thelazia, but it does not invade the eye, so it does not cause uveitis. Rather, it stays in the conjunctival sac and can cause keratitis (inflammation of the cornea) in rare cases. The AAEP guidelines recommend treating all horses once or twice a year to maintain control over parasites that are not necessarily detected by fecal egg counts. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  6. My mare is kept at a boarding stable with her own pen, but is rotated between pastures with the other horses. She was recently dewormed using a PowerPak (5 day treatment). My veterinarian found high levels of eggs both before and two weeks after treatment. Does this mean there is resistance in the parasite population at my boarding facility? What should we do next? My vet says to deworm my mare again with a different dewormer like Moxidectin. Is it bad to alternate horses between pastures, or will the worms spread between pens anyway? 

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    First of all, the parasites are already shared between horses and pens – even between farms and regions. One parasitologist has once said that North America should be regarded as one great pasture. So the horses are all exposed to the same parasite species. Resistance to benzimidazoles is extremely common in strongyles across the world, so your result is not surprising at all. But I commend you and your veterinarian for doing the right thing. You tested the efficacy of the dewormer, and because of the result, you are now changing to a different drug. Ivermectin or moxidectin are likely to still work well, but I still recommend checking the efficacy. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  7. What products would you recommend for ascarids and strongyles and how should they be administered to foals?

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    I generally recommend the products that work. It is as simple as that. Ascarids have been found resistant to ivermectin and moxidectin across the world, but some reports indicate that these drugs could still be effective on individual farms here and there. Similarly, cyathostomins (small strongyles) have been reported widely resistant to both benzimidazoles and pyrantel salts, but it cannot be ruled out that these drugs could still work on some individual farms. In addition to this, there are cases of ascarid resistance to both benzimidazoles and pyrantel salts, and cases of cyathostomin resistance to ivermectin and moxidectin. We can make a qualified guess about which drugs are likely to work in a given foal population, but the only way to really know is to test the efficacy with a fecal egg count reduction test. Also, it should be kept in mind that most foals will harbor both ascarids and strongyles at certain age ranges, and none of the available anthelmintics may effectively treat both. In these scenarios, the diagnostic information should guide you to prioritizing your treatments. Again, the way forward is to generate some diagnostic information. Anthelmintics should be administered following the instructions on the label. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  8. What is the best practice to reduce resistance in endoparasites due to deworming?

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    Anthelmintic resistance cannot be reduced once it has developed, but the rate at which it develops can be reduced. In other words, we can affect how quickly it develops. The most important factor is treatment intensity. Many people overtreat their horses with frequent dewormers administered to all horses on the farm year-round. This accelerates resistance development. The right approach is to treat the right parasites in the right horses with the right dewormer at the right time. Easier said than done, but that is the only way forward. We need to know which horses are in need of treatment at a given time point and we need to know which dewormer to choose. The only way to know this is to run fecal egg counts. This has to be done in a systematic manner and you should ask your veterinarian to help you develop a good program. In addition to this, it is important to pay special attention to foals, yearlings and youngsters. This age group of horses may exhibit different parasite infection patterns and is generally more susceptible to parasitic infection. A foal or a yearling should not be treated the same way as a horse. Finally, non-medical approaches to parasite control can greatly help reduce further resistance development. Co- and mixed grazing with ruminants has been found effective and pasture hygiene can be very beneficial as well. Strategic pasture dragging and/or mowing and pasture rotation can be effective, depending on season and climatic conditions. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  9. How effective is feeding diatomaceous earth at regular intervals? 

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    Unfortunately, diatomaceous earth has not been found to possess any antiparasitic effects when evaluated in research studies. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  10. I have a 5-year-old OTTB gelding that I have had for a year and a half. I have done three fecal counts and deworming regiments. His first fecal was done in April 2015 with results of 900. His most recent fecal, which was conducted at the end of April 2016, spiked to 1,275. I dewormed him with Zimectrin Gold and started him on a daily dewormer-Strongid C2X. I retested him two months later and he is now completely egg free. I have heard that keeping a horse on a daily dewormer can build up resistance and also can affect the digestive health and hindgut. Where do I go from here? Also, he is turned out to pasture 12 hours a day with 8 other horses.

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    I assume that your OTTB is healthy and looking good? An egg count around 1000 EPG is not unusual and there will be a few horses in most herds shedding at this level, so there is nothing to worry about here. Remember that the goal is never to keep our horses parasite-free. The goal is to prevent parasitic disease and the horses will have to live with their parasites. Your horse is a high strongyle shedder, so that qualifies him for getting additional antiparasitic treatment above the generally recommended foundation of two yearly treatments. People typically choose to deworm their high-shedding horse once or twice extra during the grazing season. Depending on climate and geography, these treatments could be applied in the spring, summer, and fall. Two fall treatments can be considered warm and milder climates. The daily dewormer is another option, which could be effective. However, your success in achieving adequate parasite control will depend on a good solution for the entire herd. The right parasite control program can be designed once we know what egg count levels the other horses are at. Then we can tailor a treatment program that provides adequate parasite control and yet minimizes the risk of anthelmintic resistance. Parasite control has to be carried out on the herd level otherwise you won’t achieve much. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  11. My two horses have never had a positive fecal egg count, and my veterinarian had taken them off deworming in 2014. This winter, my mare had diarrhea for two months, with negative fecal and bacteria cultrure results. Another veterinarian recommended moxidectin anyway, and three days later she was cured. If I want to go to a twice a year deworming program, what should I use for spring and fall without getting worms immuned to the dewormer?

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    We do recommend treating all horses once or twice a year. The point is that the egg counts mainly reflect small strongyle contamination, and there are other parasites to consider. Your veterinarian should be able to help you selecting the appropriate anthelmintics for your parasite control program, but the key is to use the drugs that work. Macrocyclic lactones (ivermectin and moxidectin) are usually a good choice. Moxidectin possesses larvicidal efficacy against the encysted larvae and can be applied in the fall. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  12. I am caring for a mare and her 2-month-old colt. He was foaled here. The owner believes the colt should be shedding and wants me to deworm him. I dewormed his mother 30 days prior to foaling and both are very healthy. When should I deworm the colt? Do foals shed their baby hair? He was born May 29th.

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    We generally recommend treating foals for ascarids (large roundworms) at 2-3 months of age. Be aware that ascarids have been found widely resistant to ivermectin across the world. And yes, foals do shed their newborn haircoat within the first few months of life. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  13. I send stool samples every six months for testing and no worms detected in six years. Can I be certain my horses are clean? We use Super Garlic DE for fly control and no flies! Does this also help with worm control?

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    No horse is ever clean, and that is not an achievable goal. But, you can be certain that your horses are low strongyle shedders and therefore require a minimum of parasite treatments. We do recommend treating all horses every year to maintain control of other parasites such as tapeworms or bloodworms. There is no evidence to suggest that garlic supplements can help control worms. Several have looked into this and the results are not compelling. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  14. I have a boarding facility and I am trying out the spring/fall deworming schedule. I dewormed with Panacur this spring, but not sure what to use in the fall? Regarding fecal egg counts, should I sample every horse or sample the pasture? Can I do the fecal testing myself?

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    While I don’t know the potential resistance status on your farm, I can say that fenbendazole (Panacur) resistance in strongyle parasites is widespread across the world and likely to present. Since this is a boarding facility, I am going to assume that the majority of horses are adults? This means that you are primarily dealing with strongyles and possibly tapeworms. Your veterinarian can better advise you regarding choice of dewormer, but strongyle control should be based on macrocyclic lactones (ivermectin and moxidectin) while tapeworms can be treated with praziquantel or pyrantel (double dose). Yes, egg counts are not difficult to do with a little instruction. I know several horse owners who have bought their own microscope and started doing egg counts. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  15. How accurate are "mail order" test kits? How long is the fecal sample viable? If I receive a questionable result, what should I do next - re-test, or go ahead and deworm?

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    We tested this in a study, and we found that if samples are kept airtight and mailed in fresh, the parasite egg counts are fine if samples are done within a week upon collection. If they are shipped with icepacks to stabilize storage temperatures, it gets even better. So, there is no reason to believe that mail order test kits should be bad or less reliable than direct analysis if everything is done properly. I am not sure what you mean by a questionable result, but retesting is never a bad idea if you have reasons to doubt the result. Just keep in mind that two counts generated from the same sample are never going to be exactly alike. If you suspect parasitic disease, you shouldn’t waste time on running fecal egg counts, but just go ahead and deworm that horse. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  16. We have six horses at our barn. They have been given dewormer approximately every 6-7 weeks. We alter what type of dewormer is given. Is this the correct frequency?

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    No, this is a serious overkill! You did not specify the age of your horses, but the large majority of adult horses do not require more than two annual treatments. Treating every 6-7 weeks year-round is a sure recipe for resistance, and you probably have a lot of it already. I recommend testing the efficacy of each dewormer on your farm and then giving your parasite control strategy a complete overhaul. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  17. Is there still a point in using drugs like Fenbendazole or Pyrantel Embonate, or is it better to stick with Moxidectin and Ivermectin?

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    Yes, there is still a point with these anthelmintics, but they will have to be used differently now. Both of these drugs have lost efficacy against small strongyles in recent years and resistance appears to be widespread. There may still be individual farms here and there where one of these might still work, but chances are small these days. However, they still have good efficacy against other parasites such as ascarids and pinworms. In addition, pyrantel is also effective against tapeworms when given in a double dose. So every dewormer still has a place in equine parasite control and should not be completely abandoned. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  18. My horse has had negative fecal counts for years and I have not been deworming. When he did not shed out this spring, my veterinarian told me to deworm him with a PowerPack. How can my horse have negative counts and still need deworming?

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    The egg count reflects presence of adult strongyle type parasites within the intestines. However, horses can also harbor encysted small strongyle larvae in the mucosal walls of the large intestines. These larvae do not produce eggs. This is probably what your veterinarian had in mind when recommending the treatment. We always recommend deworming a horse if parasitic disease is suspected. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  19. What kills adult threadworms, also known as neckworms?

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    The neck threadworm, also known as Onchocerca is a filarial parasite infecting horses. The adult worms reside in the neck (hence the common name) and the (offspring) microfilaria live underneath the skin waiting for a biting midge (Culicoides) to pick them up. There are no known effective treatments for the adult worms, whereas ivermectin has been found effective against the microfilaria. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky

  20. I do fecal checks on my horses. How reliable are they?

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    Fecal egg counts are essential for checking dewormer efficacy. If current guidelines are followed, the fecal egg count reduction test is both reliable and useful. Egg counts are also useful for determining whether an adult horse is a consistent low, moderate or high strongyle egg shedder. This pattern exists in all horse populations. Finally, egg counts are also very reliable for detecting ascarid (large roundworm) infection in foals, weanlings and yearlings. This is important as it affects the choice of dewormer. So egg counts are useful, important and necessary. However, it is important to be aware of egg count variability, which can be substantial. Your veterinarian will know how to interpret a given count. Martin Nielsen, DVM, Ph.D.,Gluck Equine Research Center, University of Kentucky

  21. I have been using fecal egg counts on my horses to determine if they need deworming. The reports have always shown 0 eggs being shed. Does that mean I do not need to deworm? I have three horses together in a barn/pasture rotation.

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    Your results illustrate that your horses are consistent low strongyle egg shedders as their results are below the detection limit of the egg counting technique used. This means that your horses require a minimum of deworming to keep other parasites such as tapeworms and bloodworms at bay. The AAEP guidelines recommend a basis of one to two yearly treatments for horses in this category. The timing of these treatments will depend on climate and the length of the grazing season. Talk to your veterinarian about the most appropriate dewormers to use for these two treatments. Martin Nielsen, DVM, Ph.D., Gluck Equine Research Center, University of Kentucky