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The Life and Times of Tapeworms

Lynda McCann is the owner and editor of this publication. She recently emailed me about a warmblood gelding that she has owned for two years. During that time Davey had been a hard keeper despite the fact that he is a stocky type horse. He also suffered a number of gas colics. This spring Davey started dropping live worms in his manure, and a small animal vet that happened to be in the barn identified them as equine tapeworms. Lynda wormed him with Zimectrin Gold and reported: “for a few days, we REALLY saw the worms!” Now his coat is shinier, and he is gaining weight. Best of all, there have been no more episodes of colic.

We don’t hear much about tapeworms and their effect on horses. Do some research and you’ll find those who say that tapes don’t bother horses much. Others claim that 50% of all colics are caused by them. So, what is the truth? The fact is yes, they usually don’t bother horses that much, and the truth also is, as Lynda found, they can bother horses a great deal. To find out how both can be true, we need to look into just what a horse tape worm is, and as we do, you will find out how to keep your horse totally safe from this parasite.

First of all, a name: Anoplocephala perfoliata. Long name, but this, our most common horse tapeworm is actually only a few inches long. Other animal tapes, including the one that affects people can be several feet long. The name tapeworm comes from the fact that they resemble a tailor’s measuring tape, long and skinny front to back. Most other worms that inhabit horses are round, like earthworms. The round worms include ascarids and large and small strongyles, the ones that we commonly worm for.

The equine tapeworm is probably the strangest creature that God put on earth. First, there is really no head. There is a front end, which contains 4 hooks so that the tapeworm can latch on to horse’s intestinal wall. There are no eyes or ears or other sense organs that we know of. They don’t need any of them to survive and flourish. The most amazing thing is that there is no mouth or digestive tract. The tapeworm simply absorbs all the nutrition it needs through its outer covering. This is important to note as that is what is targeted when we deworm for tapes.

After the adult tape worm attaches to the gut of the horse, it just dangles in the horse’s intestinal contents and takes what it needs, 24/7. Behind the front section there is a long chain of segments. The tapeworm has been described as a freight train with lots of boxcars hooked together in a line. Each of the segments has its own complete reproductive factory to make eggs. Perhaps we should call all tapeworms “she”, because there is no male involvement. As the eggs in the last segments mature, the caboose (the last segment) drops off and that package, filled with eggs, goes out with the manure. When the eggs in the “new caboose” are ready, that segment is released.

There is an area of the horse’s intestine where the small intestine empties into the cecum. The cecum is like our appendix except that it is very large and is important in fiber breakdown. There is a valve that prevents back flow from the cecum to the small intestine. It is the spot where all where the tape worms hook on and literally hang out. It’s not a big area, and so if a horse has tapeworms the cluster of them will be found right there. If the group is small, let’s say 20, they may not be a problem. One or two hundred may be more than irritating and can cause some serious colic issues, some of which can only be fixed by surgery.

So, to summarize. An adult equine tapeworm stays hooked in its permanent spot and is continually bathed in the horse’s intestinal contents. The tape’s food is absorbed through its “skin”. No digestion is needed, the horse has already done that. The hind egg segments drop off when the eggs are mature. Now, some questions remain. What happens to the eggs after they go out with the manure, and how do horses get infected in the first place?

Unlike the human tapeworm, the equine tapes need a friend, another host . That “intermediate host” is a tiny creature, the Oribatid mite. It is about the size of the period at the end of this sentence. These beetle-like bugs live by the thousands in every square foot of soil and are just as important as earthworms in breaking down organic matter. As the mite works its way through the soil, it might come on a real treat, an egg loaded segment from the tapeworm. Tapeworm eggs hatch inside the mite and become tiny larvae. The mite is apparently not bothered by them. The mites also crawl up vegetation, and that is where the horse is apt to pick them up in a mouthful of grass. The horse digests the mites, and the tapeworm larvae are released into his gut. It takes several weeks for the larvae to turn into adult tapeworms. The adults hook on to the horse’s intestine in that very specific place, grow into adult size, and the cycle starts again.

Your veterinarian probably is encouraging you to take once or twice yearly fecal samples and worm according to what is found. Those reports are on the round worms that have always been a problem in horses. Round worms are continually releasing eggs into the horse’s digestive tract. Tapeworms are different in that whole segments of the worm are being released, and the release is more sporadic. As a result tapeworm eggs are rarely seen on fecal exams. The other issue is that when we do fecal exams for parasites, we use concentrated solutions to separate and float the eggs, and, wouldn’t you know, tape worm eggs don’t float. So, the absence of tapeworm eggs found in the lab does not necessarily mean no tapes.

There are reports in the literature of a blood test that can be run to detect the protein of the tapeworm, but it is used mostly in research. Most vets take a practical route in dealing with potential tape worm problems. In our practice we often recommend worming twice a year with one of the dewormers that is effective against tapeworms. We have found, for our part of the country, as long as good manure management is being practiced, twice a year is often sufficient worming to take care of all intestinal worms, round and tapeworms. There are four wormers available that are effective against tapes. One is the old standby Strongid . You need a double dose of the paste to get most of the tapes with this wormer. The other choices (Zimectrin Gold, Equimax, and Quest Plus) contain Praziquantal which is very effective against tapes and is very safe. Praziquantal works by affecting the outer covering of the tapeworm. Then unable to absorb nutrients the tapeworm dies and passes out with the manure. With hundreds of tapes this die off may take a few days. Incidentally, the most popular wormer of today, ivermectin, has no effect on tapeworms. However, used in wormers that combine it with Praziquantal, tapes, round worms, and bots are all taken care of.

Good manure management is part of parasite prevention. This means picking up poop regularly, and pilling it to compost someplace where the horses can’t get at it, and leaving at least 6 feet all around the pile away from horse grazing. This prevents mites and the larvae of round worms from reinfecting the horses on your farm.

Lynda’s horse Davey had spent his life on 24/7 turn out until she took ownership. My guess is that it was a big pasture with no attempt at manure clean up. He had probably never been wormed with one of the products mentioned above. He was the perfect set up for a heavy infection of tapes, as evidenced by the tapes being passed spontaneously. There was just no more room, and so some had passed even before he was dewormed.

The take home from all this is that, in the New England states tapeworms in high numbers can cause unthriftiness and colic in your horse. Chances are most horses that have never been dewormed for tapes are carrying them. I think it makes good sense to use the wormers mentioned on a rotational basis twice a year to insure that your horse is free. The wormers mentioned do kill round worms as well, and I would rely on your vet to suggest the proper rotation. The ingredients and concentrations are unique to each product.

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