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Posted by: admin on Oct 19, 2009 - 11:00 AM
equinehealth
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Everyone answers, “Yeah, my horse is regularly dewormed.” But these days it doesn’t mean that your horse isn’t still burdened with parasites. Wild horses had the right idea. They dewormed themselves by the low levels of toxins in certain weeds they grazed. Too bad it ain’t free these days. No horse is going to be free of parasites, but we should be educated to know how to control the numbers in our herds. What product to use, when to use it and what it is that we are killing are important questions. Also, what else can I do as a horse owner to limit parasite numbers on my farm?
1). Roundworms (Parascaris equorum), the long worms that you see coming out of your weanling or yearling. The earliest age that youngsters are affected is 3 months considering the worm cycle, so don’t deworm your 2 week old colt. We recommend first deworming for roundworms at 8 weeks old and thereafter treating every 6 weeks. The product? Well, that depends on what you suspect the worm burden is. If the weanling is skinny with a pendulous belly and lethargic, then he probably has more rounds in him that the active weanling of an appropriate weight. So treat the heavily parasitized youngster with Fenbendazole first, then six weeks later go to the more effective Ivermectin. Note that when you treat with Fenbendazole (panacur) specifically for roundworms, you treat with a double dose (10mg/kg) once daily for five days; Ivermectin is the regular dose given once. If you treat the heavily parasitized weanling with Ivermectin, then you could potentially cause a massive die off of the worms and possible impaction of the small intestine. Plus the worms are antigenic and can stimulate a pretty big inflammatory response. The lifecycle of the roundworm larvae involves migration through the lung tissue among other places. Some of these youngsters may also exhibit a cough and snotty nose. Older horses usually more than 1-2 years old tend to gain immunity to roundworms, their immune system may inhibit the migration of the larvae through different stages.
2. Large strongyles (Strongylus vulgaris), not so much a problem since the introduction of ivermection. Aka the bloodsuckers, these larvae migrate through the vessels that supply blood to the intestine causing blood clots and possible death of the intestine. But they could potentially be a problem in areas that don’t have any type of deworming protocol. Recommend Ivermectin to treat with.
3. Small strongyles (Cyathostomes), the larvae of this worm can cause serious diarrhea in horses. Diarrhea associated with these worms is typically seen in late winter or early spring as the encysted larvae in the large intestinal wall excyst. This results in quite an inflammatory response, altered water absorption and watery diarrhea. Moxidectin is pretty effective at killing cyathostomes, recommended to deworm prior to the winter months to decrease larvae numbers. Remember, don’t give moxidectin to weanlings under 5 months of age, as it can have toxic side effects. Can be troublesome to diagnose if infected with the larvae since they are encysted in the intestinal wall. With diarrheal cases will usually see the red worms in the manure.
4. Tapeworms (Anaplocephala perfoliata), high numbers can cause problems in the horse. They have a predilection for the junction between the small intestine and the cecum, attaching to the intestinal mucosa. They may cause enough mucosal ulceration to cause a mild anemia, it’s debated whether they are involved in intussusception (one part of the intestine telescoping into another part). The worm segments look like rice grains. They are eliminated periodicially, so a fecal float may not always show an infected animal. Praziquantel is the dewormer of choice for tapes, recommend deworming with Praziquantel once every six months (twice yearly), give at least one dose around fall time.
At least once yearly your veterinarian should take fecal samples of a percentage of the horses (doesn’t have to be all) on your farm to see whether your deworming protocol is effective. All horses on the farm should be on a similar deworming program and horses dewormed around similar time intervals. Programs are going to be different on each farm, the above are just recommendations. Fecals can also be used to see whether you can decrease the frequency of deworming in some situations, which may decrease the chance of resistance problems on your farm.
Manure control is also important. Manure collected and spread on the pasture just allows parasites to enter their cycle again. Composting is a great option to parasite control. The heat kills worm larvae, as well as also controlling fly larvae and eggs. 3ft by 4ft compost piles that are rotated periodically to mix the compost will usually be complete by 3 months so that the compost can then be spread on the pasture. For the horses already out to pasture, raking the field to break up the manure will allow the sun to dessicate or dry out some of the larvae. Roundworm eggs are difficult to eliminate once in the environment. They can potentially remain infective in the environment for up to 5 years.
If you have any any questions concerning deworming strategies, then please feel free to contact your veterinarian or any of the doctors at New England Equine Medical & Surgical Center.
Karyn Labbe, DVM
Jacqueline Bartol, DVM, DACVIM
www.newenglandequine.com
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