Fighting Powerful Parasitic Predators

Having thoroughly evaluated your management and environment set up for your horses, as we discussed last month, you’re now faced with setting up a deworming program.

This was simple in the ?old days.? In the ?very old days,? you scheduled your veterinarian to come twice a year and tube your horse with dewormer. Then along came paste dewormers. In those ?old days,? many horse fanciers then set up their own programs and gave all their horses paste dewormers (faithfully rotating them) three or four times a year.

So what’s the new improved way to handle parasites and your horse’ First, management strategies, as discussed last month. Second, learn about fecal egg counts (FECs).

THE EGG COUNT.? Fecal egg counts are similar to having your small-animal veterinarian do a check of your dog?s stool for parasites. In small animals, the goal is no parasites at all. So the fecal exam for your dog simply looks for any parasite eggs. That is a qualitative fecal exam.

Attaining complete freedom from parasites is unlikely in your horse and may not be ideal anyway?a few parasites help to stimulate natural immunity to parasites in your horse. So a fecal exam for your horse is looking at the actual numbers of parasite eggs?the fecal egg count or FEC. This is a quantitative exam.

The vet or veterinary technician at your vet?s office will take a set amount of manure, mix it with a flotation solution and put it into a special slide with a counting grid?called a McMaster slide. Counting the eggs seen will give you a quantitative evaluation of your individual horse’s parasite infestation. A horse with a low FEC?say 100 to 300 EPG or eggs per gram of manure?will have a different deworming schedule than a horse with a high FEC, say 500 to 1000 or more EPG.

WHY BOTHER’? Your first reaction may be that doing all of these FECs, especially one for each horse, is going to be expensive and time-consuming. You?re right, initially. But, in the long run, FECs will save you money and are better for your horse’s health.

The cost of having this done by your vet will likely be under $25 for each sample. You may save money sending a sample to a mail-order lab, but the drawback to this is that the sample can dry out during its journey, which may result in an incorrect lower count.

With an accurate count, you and your veterinarian can identify the horses who are shedding most of the eggs that contaminate your pastures and causing all the horses to be re-infected. Those horses will need, and should receive, more doses of dewormer than the low FEC horses.

Overall, your dewormer cost will go down as you reduce unnecessary doses for the low FEC horses and concentrate on treating the problem horses?those with a high FEC.? This will also aid in your fight against parasite drug resistance.

TREATMENT OPTIONS. Once you have identified the low and high FEC horses, you can start to plan what dewormers to use and when. Most low shedders will get away with being treated twice yearly.

These horses can get moxidectin with praziquantel twice a year and be covered for everything from all strongyles to bots, roundworms, pinworms and tapeworms. Already, you have saved by cutting out two or three additional dewormer drugs. Depending on where you live, the exact ideal time of year to use these medications will vary somewhat, such as after the first hard frost. (Note: Take special care using moxidectin to be certain you have an accurate weight for your horse, especially if you’re treating smaller equines, so you give the correct dose. Do not overdose.)

The high shedders will need more treatments. Five dewormings per year are recommended. Two of these dewormings would be moxidectin and praziquantel, just like the low shedders would receive.

In addition, your veterinarian may suggest doses of oxibendazole, ivermectin with praziquantel, or pyrantel throughout the year as well. The exact drug rotation can be determined by you and your veterinarian by looking at fecal egg counts both before and after dewormings (see deworming drugs chart). Any resistance in parasites on your particular farm will soon become evident.

BOTTOM LINE. It involves labor, but the most cost-effective thing you can do in your deworming program is environmental (see February 2012). After that, we believe diligence to fecal egg counts will pay off in the long run, especially if you plan to keep the same horses for years. Focus your protocol on the horses who need the most help and target your drug choices to the parasites you need to control.

The Safety of Other Animals: Remember the potential danger of some of the dewormers to dogs with the genetic MDR-1 defect (see November 2011). The apple-flavored dewormer paste is particularly attractive to dogs. Make sure your horse consumes all of his paste and ideally keep your dog out of the barn and away from any manure for 48 hours or so.

Alternative Dewormers: The use of alternative dewormers such as black walnut may appeal to your sense of natural care for your horse. don’t do this! There is virtually no regulation of these alternative dewormers. Most of them are potentially toxic to your horse. In addition, exact dosages are not worked out. With a lack of FDA regulation, many alternative medications have been found to have variable concentrations. The dewormers listed in our chart are well-researched and found to be safe for almost all horses.

Saving On FECs: If you’re part of a horse club, you can take a lesson from dog owners and organize a clinic or set up a volume discount with your veterinarian. If everyone from your barn drops off a sample on the same day, your clinic can have a veterinary technician set up to deal with all those samples at once. You could also organize a fecal clinic.

And, of course, you can purchase supplies and learn to do fecs yourself (see October 2009 issue). The microscope is the most expensive piece of equipment at $125+, but perhaps you could share one with a group. you’ll need to know what you’re looking for, so you can offer to pay your vet or a vet technician to teach you how to do this.

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