Skip to main content

Internal and External Equine Parasites

November 2017 - AAEP is on Stall Rest

AAEP is taking the month of November off from "Ask the Vet", but will be back in December to answer your equine health questions concerning winter weather care for your horse with expert, Dr. Christine Tuma.



Click here to read this month's questions and answers.
  1. I have three Tennessee Walking horses and all three now have mane loss underneath the mane /forelock and some tail loss. I have checked selenium levels, which are normal, no parasites, no fungus, no rubbing and no ticks. The mane loss is only from the underside. This happened to one horse 10 months (on-going) ago , then 2 months ago my mare and now 7-year-old gelding. They are on fesuce pasture and hay, little grain and regular deworming schedules with regular fecals showing them clean. Two of the horses have been in the same environment for 7 years, the other and last to show symptoms came in Oct. 2013.We live in the Piedmont area of North Carolina.
    I am assuming some contaminent but what? I changed grain in case that was the problem but hair loss began in last horse after grain change. They get very little1 lb. day in the summer. They have salt block, no supplements.
    Advice?

    (View Answer)

    Skin/hair coat problems can have a multitude of causes that can be very difficult to sort out on your own: infections, infestations, contact with foreign substances, and allergic reactions can all cause such signs. Direct examination of the skin through biopsies and/or scrapings of the affected areas might help you get at the root of the cause. Sounds like something that you should have your veterinarian take a look at! David Ramey, DVM, Encino, CA

  2. I have a 12-year-old gelding that has a VERY swollen sheath with no swelling elsewhere. He recently has gone from being stalled 11 hrs a day to turned out 24/7. There are also bite marks on the sides of his sheath. He has also been rubbing the sides of his face raw. I fly spray him twice daily and he is dewormed every 6 weeks. He has recently rubbed a portion of tail hair off. Could he be allergic to gnats?

    (View Answer)

    With bite marks and swelling, I'd be concerned about inflammation and/or infection. Sounds like the sort of thing that you should call your veterinarian to examine, as soon as possible! David Ramey, DVM, Encino, CA

  3. My horse has been confirmed (76%) by UC Davis as having EPM. I am giving him Marquis. Is there any other way besides oral dosing him to get the medication in his system? He has terrible problems with his mouth and this is a daily "torture" treatment.

    (View Answer)

    Marquis, the Bayer product, is only available in a paste formulation. Unfortunately, as you know, not all horses are wild about having paste squirted into their mouths. Getting the assistance of an experienced horse handler might certainly help. There are other medications for EPM - sulfa and pyrimethamine tabs come to mind - but you'll want to consult with your veterinarian as to whether they might be good options for your horse.

    Unfortuanately, while a particular medication may be a good option, it's not always an easy one! David Ramey, DVM, Encino, CA

  4. When treating horses for persistent pin worms, I was advised to deworm using a paste in the rectum. Do you advise this, and what dewormer would get the best results? Also, how often can this be done?

    (View Answer)

    I am aware of this treatment, but I don't know of any studies evaluating it. It is my understanding that people use fendendazole paste, which should be quite safe. I would probably go with either moxidectin or ivermectin dewormers orally. They are very safe, as well.  Make sure you remove parasite eggs by thorough bathing of the rear end, too! David Ramey, DVM, Encino, CA

  5. I am the only boarder at my new barn. It is very clean and manure is picked up daily, even in the grass paddock. At my last barn, I had a fecal count done twice a year and dewormed accordingly. I always use Zimectrin after the first frost, and twice a year, spring and late summer I use a dewormer with Prazi Quantel. Should I change my deworming routine since I am the only boarder? I still intend to do a fecal count this fall at the time of vaccinations.

    (View Answer)

    I would certainly consider changing your routine, especially since there aren't other horses around to provide other potential sources of infection. Keep up the fecal counts! David Ramey, DVM, Encino, CA

  6. Because "pinworms" do not show on fecal tests, what is the best way to make sure my horses do not have pinworms and how can I keep them from getting them? If they have pinworms, what is the best way to get rid of them.

    (View Answer)

    Pinworms are bothersome parasites that cause very little actual damage to the horse.  But while they're not dangerous, they can certainly be a pain in your horse's butt.  Adults crawl out of the horse's rectum to lay their eggs, which can cause intense itching.

    Severe itching and hair loss can be a sign that a horse has pinworms.  Occasionally you can make a diagnosis by seeing adult pinworms around the rectum.  The test for pinworms is the "Scotch tape" test, where you touch the sticky side of cellophane tape around your horse's anus, and see if it picks up eggs, but that test doesn't always find eggs.

    Common orally-administered deworming agents such as ivermectin or pyrantel still have pretty good effectiveness against pinworms, even though resistance to such agents is reported.  I've heard of some people putting deworming paste in rectally, as well, in an effort to increase the local concentration of dewormer (but I have no idea if it's effective).

    Prevention of further infection also relies on devoting time to keeping your horse's rear end clean.  You should also decontaminate areas where horse's might rub (and leave eggs) such as fence posts, walls or other surfaces.  Use a wire brush and a safe disinfectant.  Of course, keep feed and water sources cleaned out, too (which you'd want to do anyway, of course). David Ramey, DVM, Encino, CA

  7. My horse has had a couple fecal egg counts, all being negative and no need to treat. I haven't treated for a year and have another test coming up. If it's still negative, I'm not sure if I should at least treat for tapeworms since those don't show up in the egg counts. Would this be a correct treatment?

    (View Answer)

    You're right that looking for eggs in your horse's feces is not a reliable way to detect tapeworms, but it's still worth a look.  Even though fecal floation tests aren't consistently reliable, there is a very effective blood test that looks for a specific tapeworm protein antigen, and I'd certainly consider that test, if you're worried. You can also sometimes see segments in a horse's feces, especially after you've given him a deworming agent.

    There are a couple of reports on increased incidence of colic in horses with tapeworms, but it's pretty hard to find other instances of ill effects. Bottom line, though, is that if I were in your shoes, before doing anything I'd ask your veterinarian, or contact your area veterinary school, and ask about the prevalence of tapeworms in your area. Studies have shown that they are very rare in certain areas - very common in others. And certainly think about running a blood test if you're concerned.  

    Tapeworms are certainly not benign, and it's easy to treat for them using easily available dewormers. You can learn a lot more by reading the article on the AAEP website at http://www.aaep.org/info/horse-health?publication=877David Ramey, DVM, Encino, CA

  8. Since Bots do not show up on a fecal egg count, should a horse regularly be dewormed for bots or only if you find the eggs on their hair? Of course, removing those eggs on the hair is important too. In addition, what about encysted strongyles, do they show up on a fecal egg count? How do you tell if your horse has encysted strongyles even at a subclinical level?

    (View Answer)

    Bots seems to cause horses very few problems. Like you said, they don't show up in fecal egg counts - the easiest way to diagnose them is by the presence of bot eggs on the hairs of the lower limbs. In areas where bots are prevalent, people typically deworm for them 30 days after the first frost, when the adult flies are no longer active. Ask your veterinarian about the prevalence of bots in your area.

    Encysted strongyles differ from other equine parasites in that their development can be arrested when the encyst in the horse's large intestines. They can remain in the wall of the horse's gut for as long as two years. Typically, they encyst in cooler months, and emerge once the weather warms up - the timing reverses in tropical climates, where heat stress is the problem. The most important risk factors are age of the horse (young horses are most vulnerable), season of the year, and how long it's been since your horse was last dewormed.

    You can't tell if your horse has a subclinical infection. By definition, subclinical means that it's below the level of clinical detection. But by checking for cyathostomins at the right time, when they are emerging from their encysted stage, and using effective deworming agents as prescribed by your veterinarian, you can do a lot to control the problem. David Ramey, DVM, Encino, CA

  9. My horse is perfectly fat and healthy, but on her neck and chest she has a lot of dry skin hanging. Her mane is still thick. Could this be parasite related?

    (View Answer)

    While "dry skin hanging" doesn't bring any condition immediately to mind, there are certainly parasite problems, both internal and external, that can result in skin-related problems.  Of course, there are also many skin problems that aren't related to parasites, and it's not always easy to tell the difference between those that are and those that aren't. This sounds like the sort of thing that you should have your veterinarian look at, to see if you can come up with an underlying cause. David Ramey, DVM, Encino, CA

  10. My six-year-old Arabian had an adverse reaction to a particular deworming medicine this spring. He developed a swelling on the left side of his mouth where I ejected the paste within less than 30 minutes. His lower lip and side of his mouth became swollen and I immediately called the veterinarian. We ran water on the swollen lip and monitored his breathing. We applied Cortisone 1% on the outside of his mouth and face as prescribed by the vet. The swelling went down over the next three days. My question is, what do I use for a deworming medication now?

    (View Answer)

    Reports of reactions such as you describe are extremely rare, but I certainly understand if you wouldn't feel comfortable using the paste again.  

    Fortunately, you have several options. Ivermectin liquid can be dosed through a nasogastric tube by your veterinarian. And, of course, there are several non-ivermectin-based products out there, such as various benzimidazoles, pyrantel pamoate, or moxidectin.

    You should also ask your veterinarian do do periodic fecal egg counts to see how well your dewormer is working. Depending on your horse's circumstances, you may find that you may not need to deworm as often as you think. David Ramey, DVM, Encino, CA

  11. Everything I have researched says to not deworm regularly anymore and perform fecal counts first. That said, we now do fecal counts twice a year. What is your opinion on this?

    (View Answer)

    I think what you're doing is great. Checking twice a year, and deworming only the moderate and heavy shedders is certainly the way to go. It's better for the horses, and it's better for the environment, too! David Ramey, DVM, Encino, CA

  12. I have a companion donkey. My horse contracted lungworm. Do you believe horses and donkeys can be kept together?

    (View Answer)

    Lung worms are a pretty unusual problem in horses in the United States. When they do get infected, it is usually from donkeys. Donkeys infected with lung worms usually show no clinical signs of disease. In horses, the parasites only very rarely can complete their life cycle, so the transmission almost never goes the other way.

    It's harder to make a definitive diagnosis of lungworms in horses than it is in donkeys. With donkeys, diagnosis can be made with a fecal test, but that generally doesn't work in horses.

    Donkeys and horses can certainly be kept together, but you'll definitely want to test them, and deworm as appropriate. Ivermectin dewormers are usually effective against lungworms. Work with your veterinarian to come up with a problem that's ideal for your setting. David Ramey, DVM, Encino, CA

  13. What is the optimum time frame a person should deworm their horse and should the product vary to get all types of parasites? I have friends who believe you should deworm every month and others think it is bad for the horse.

    (View Answer)

    The good news is that deworming agents are, in general, extremely safe, so they really aren't ever "bad" for the horse, in the sense that you're unlikely to hurt him by giving him a dewormer. The bad news is that resistance to deworming products is becoming quite a problem, and deworming all the time helps parasites develop resistance. Plus, it's bad for the environment. That's why it makes sense to work with your veterinarian to develop an individualized program based on fecal egg counts for your horse, and to deworm only when needed.

    There isn't a "right" answer to your question - every horse should be treated as an individual. Work with your veterinarian to find out what your "right" answer is. David Ramey, DVM, Encino, CA

  14. I perform fecal counts on my gelding both fall and spring but honestly I don't know what I should be doing. Generally he's clear just as the test results indicated this spring. Does that mean I do nothing in between fecals?

    (View Answer)

    No need to do anything between fecals if he is testing clear. Generally, no need to deworm unless he has a moderate parasite load, either. Many horses develop an immunity to internal parasites - maybe you have one of those! David Ramey, DVM, Encino, CA

  15. What is the best current deworming protocol for a boarding facility. I know that monthly rotational deworming is not best practice, but for a facility that potentially has horses coming and going, what would the best recommendation be? Fecal counts and then treat for what you find?

    (View Answer)

    If you’re running a boarding facility, I'd suggest testing, and ideally quarantining, each new horse that comes in, and deworming accordingly.  If you have lots of horses on your facility, use fecal egg counts every few months to check for shedders. Select the moderate and high egg shedders for deworming, and only treat those horses (your veterinarian can get the fecal egg counts done for you). You don’t need to test all of the horses, but you should test at least six to get some idea of how things are. If your facility has horses in more than one pasture, I'd suggest testing some in each pasture. And then, only treat horses with signs of a heavy parasite load. David Ramey, DVM, Encino, CA