If the horse at left was at my barn, the first question I would ask would be: when was the last time she was dewormed?
Why? Well, she's got a bit of a potbelly, but you can see her ribs. She doesn't have a whole lot of "shine" to her coat even though it is summertime, and her topline and hips indicate she's not in the best of physical condition. If she's being fed on a regular basis, there is some reason why she's out of condition, ribby, and potbellied.
Around here, some people believe in the "twice per year" cure. Probably the same everywhere. So, let's talk about the holes in that theory, and why you might be overdoing rather than under-doing.
1. Do you have your horse(s) at home/in an isolated environment, or do they share a pasture/stall/barn with several other horses owned by different people.
This is important because if you have your own horses on your own property - there is no cross-contamination from outside horses, new boarders, or boarders who may deworm less frequently or less effectively than you do.
2. How old is your horse?
Foals and yearlings are more susceptible to certain types of worms than older horses, and studies have shown they should be on a more frequent deworming schedule.
3. Where do you live?
North, south, east or west...Different flies (and therefore different worms) are more prevelant in different areas. Likewise, if you live in areas with high deer populations, you absolutely, positively should be deworming for tapeworms twice a year along with using other standard products. Depending on your area, certain types of worms have developed a resistance to certain types of dewormers.
4. How often should I deworm?
Part of this answer is determined by the above questions. Two times a year with ivermectin just flat out doesn't cut it. If your horse lives in a mixed populations, more often is indicated. If it's just your horses, you can probably get away with a little bit less, although some experts may argue this point. If you clean the manure from your paddocks, or you have very few horses per very large acreage, you are in a much "cleaner" position than the barn that squeezes 3 horses per dirt lot.
5. So what about this whole "parasite resistance"?
When you deworm, don't under-dose. Use the entire tube, unless you are using Quest which requires a bit more care. All these dewormers have toxicity levels much higher than a single tube. Exceptions are minis and small ponies, which I would more carefully dose by weight. But if you have an 800 pound horse and you give him the 1000 pound dose of dewormer - it's not going to kill him.
So how do I know if my horse has worms? And why should I worry?
Well, the easy answer is: every horse has some level of worms, at any given time. The question is, what kinds, and what product should you use? The long answer is: a fecal, inexpensive at your vet's, will determine which types of worms your horse has, which will tell you which product to start out deworming with. Or you can jump in blind and start with one product, but rotate every 2 months and monitor your horse's condition.
The whole point of deworming is to kill off the parasites before they build to a harmful level. Some adverse affects of heavy worm load are poor hair coat, generally poor condition, anemia, colics, and long-term harm on the digestive tract.
I hear you saying...ok, but I'm still confused about all this.
Deworming on a rotation is key. You want to rotate by ingredient, not by brand. Most vets now say every 2 months is a good plan.
Ivermectin kills basically everything except tapeworms and encysted small stronglyes. It's a good base dewormer, and it's non-toxic to several times the weight-dose. I usually give an entire tube when I deworm my horses, just because they are bound to spit/drool/rub some out - at least my appaloosa enjoys doing so!
Ivermectin is sold under the names IverCare, Zimectrin, Equimectrin, Bimectin, Equell, and Rotectrin, among others.
Pyrantel Payomate kills large and small stronglyes, roundworms, and pinworms. It is a "softer" dewormer, with a more narrow spectrum of what it will kill. If I buy a new horse with an unknown or questionable deworming history, I will deworm with a Pyrantel dewormer first.
Pyrantel is sold under the brand names: Strongid, StronglyeCare, Exxodus, and Rotectin P.
Fenbendazole kills large strongyles, small strongyles, pinworms, and ascarids. If your vet recommends a "Power Pac", you will want to do 5 days in a row of a Fenben dewormer. This is a super-safe dewormer that is excellent at clearing out persistantly wormy horses.
It is sold under the brand names: Panacur or Safe-guard.
For tapeworms, there are two products on the market that contain praziquantil, which kills tapeworms plus Ivermectin, discussed above. These are Zimectrin Gold and Equimax. Spring and fall are the recommended times to use one of these products to take care of tapeworms, if they are a problem in your area.
Finally, I want to mention Moxidectin (sold as Quest); Moxidectin plus praziquantil (Quest Plus) and the daily dewormers (Pyrantel Tartrates).
Quest and Quest Plus have received a lot of bad press: but Quest is not the problem. Moxidectin kills everything but tapeworms, and it kills effectively. If your horse has not been on a regular rotation, do NOT use Quest until you get him on a rotation. The problems people experience with Quest is the worm die-off it creates, and a subsequent colic in the horse. Likewise, Quest Plus kills everything, period. I use both products, and have used them for three years on several different horses, without an issue. BUT, I have followed a rotation recommended by my vet, for my area and been careful. This is the one dewormer I will dose carefully by weight and not just walk out in the field and shoot the entire tube into their mouths.
On the reverse side of the spectrum: daily dewormers don't kill a whole lot. You cannot rely on them to be your entire deworming program. You still need to rotate in an ivermectin-based product, and deworm for tapeworms as well, when using a daily product.
Are there exceptions to all this? Sure. I know of a 6-year-old gelding who probably had never been dewormed in his life, was dewormed by a new owner with a regular dose of ivermectin. He had an instant allergic reaction, basically like a seizure. It was over in a minute, and he was physically okay - but it took vigilant daily deworming (PowerPac), plus more ivermectin, then on a monthly rotation, to clear up all the worms in the poor guy's system.
As always, discuss your plan with your vet - a phone call is free, and he/she knows your horse and your geographic area. I do not :)
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