Healthy Low-Risk Adults
This is the group where routine dewormings on a schedule are least likely to be needed and most likely to cause resistance problems.
• If the horse is on turnout, consider routine timed dewormings only during the grazing season, checking fecal egg counts once during the winter to see if additional deworming is required. The last deworming of the season should target bots and tapes.
• Alternatively, the horse may be dewormed with a comprehensive product, including bots (not detectable on fecal) and tapeworms twice a year, with fecal checks in between to see if any additional treatment is needed.
Bottom Line
The ready availability of dewormers directly to owners is convenient and economical, but your vet is still your best source of advice on the deworming program that is right for your own situation.
If your horse is low-risk (not under stress, has a healthy immune system, doesn't travel and isn't on a farm with lots of new horses in and out), you're probably better off relying on fecal counts to determine your deworming schedule. However, if this is just too much of a nuisance for you, back off a bit and deworm less frequently. Note: Bots and tapeworms aren't easily detected on fecal exams and require specific dewormers.
Until research tells us otherwise, stick with ivermectin or moxidectin, as they have the lowest likelihood of resistance developing, and both of these dewormers also target bots. For tapes, you'll need to use double-dose pyrantel pamoate or a drug containing praziquantel. We recommend twice-yearly tape deworming schedules. In fact, for some horses, twice-a-year with a broad spectrum dewormer that targets bots and tapes may be sufficient.
If your horse is high-risk, by all means, get the veterinarian involved until you have the parasite problem under control. It's foolish to keep throwing dewormers at this horse without knowing what types of pests you need to target.
If the horse is heavily parasitized, and hasn't been dewormed in a while or you don't know its deworming history, you may want your vet to pre- and post-medicate the horse with Banamine and/or an antihistamine. This will help reduce the risk of adverse reactions to the large parasite die-offs.
In choosing a brand of deworming drug, check the package labels carefully to ensure that the actual active ingredients of the drugs-and amounts of those drugs-in the specific products are the same. If they are, let price be your guide in choosing among brands.
Try to get an accurate measurement of your horse's weight. Underdosing your horse is a waste of time and money, as it won't work effectively. The option of "more is better" is not always wise, especially if you're using moxidectin, which has a lower safety zone than other dewormers. Follow label instructions on all drugs, and get a weight-tape if you're not good at estimating weight.
Many people religiously drag their pastures to break up manure piles, the rationale being that this exposes the larvae to the deadly effects of drying. However, there are also experts who say all this does is spread the larvae around in a wide area. Without dragging, larvae remain heavily concentrated close to the manure piles. Since horses will not graze around their manure piles, the problem takes care of itself. However, several factors come into play here:
• Horse density. If your horses are out on large pasture (2+ acres per horse), dragging may be counterproductive, since they likely have enough manure-free areas to graze and will avoid those spots. With crowding, exposure to larvae is much more likely and dragging may help reduce the larval populations.
• Weather. Dragging should be timed for a period when the weather is hot and no rain is expected. These are the conditions most favorable to the larvae dying of exposure.
• Turnout options. If you are going to drag, the horses should be kept off the pasture for a week or two, to allow eggs to hatch and larvae to die. Otherwise, all you are doing is contaminating all their grazing area. If other turnout facilities aren't available, consider dividing the pasture with temporary fencing and dragging by sections.
• Grass height. Dragging when grasses are dense and high is not likely to be effective since the grass will trap sufficient moisture at ground level and protect the larvae from sunlight.
If your turnout area is relatively small, daily removal of manure is the ideal management.
For larger fields, strip grazing is a good idea. The area is divided into two or more sections and horses permitted to graze until the grass is eaten down to a specific height (consult your state agricultural extension agent for recommendations). At this point, the horses are moved to another section of the field. Dragging does have the advantage spreading the "natural fertilizer" across the field, which helps to avoid the dense hillocks of uneaten grass that grow in the area of manure piles.
