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TwendeHaraka 11-03-2009 07:38 PM

I recently moved my horse to a new barn, and suddenly I've taken on a whole bunch of responsibilities that I never had to worry about before. I feel stupid for asking, but I need to find out.

How often do you worm? I'm fairly certain at my old barn, they wormed every month during the summer and every other during the winter, but how often should I worm him?

How often do you switch wormers/What to worm with? I know you aren't supposed to keep worming with the same thing every time, but how often should I switch it up? Every time, every other? And what exactly is the best thing to worm with? I've been worming with Ivermectin and Praziquantel, but should I switch that up too?

I need to figure these things out, and I'm glad that I'm finally getting the chance to learn them, but I need a little help. [: If you have any good websites that I can read about worming, that would be great, too.

WelcomeStranger28 11-03-2009 07:41 PM

I worm my horses every first day of the season!!
i hope you find out!!!

TwisterRush 11-03-2009 07:52 PM

my horses are done every 6 weeks. it also depends where you live, how old your horses are etc..

here is an article you might find useful :

WikiAnswers - How often do you have to de-worm a horse

Ryle 11-03-2009 07:57 PM

For 40 years now, veterinarians have recommended that horses be dewormed every 8 weeks all year round and rotation of dewormers has been recommended for nearly that long. This is considered by many vets and horse owners to be “the recipe” for adequate and appropriate deworming of horses. However when you look at the research that has been done in the last 15 years you really have to question this practice. “’The recipe’ no longer represents an acceptable program for strongyle control” according to Dr. Craig R. Reinemayer, DVM, PhD of East Tennessee Clinical Research, Inc during a webinar presented via This means that deworming recommendations for adult horses need to be reconsidered because strongyles are the only significant nematode pathogen of mature horses. Continuing to use the same old deworming program will likely lead to heavily parasitized horses and further drug resistance. Instead, each horse and each situation should be evaluated to determine the reinfection rates and an appropriate deworming program for the individual.

There are 4 classes of dewormer on the market:
benzimendazoles --fenbendazole, oxibendazole, other chemicals that end in -azole (there is a long list)
pyrantels---pyrantel pamoate (paste) and pyrantel tartrate (daily dewormer)
avermectins---ivermectin and moxidectin

Of those 4 classes, all but praziquantel are "broad spectrum" meaning that they kill several types of parasites. It is not necessary (or at least was not prior to the developement of parasite resistance) to rotate dewormers using these products to kill the most common parasites of horses. The "rotate to kill the different types of parasites" was necessary when we only had the much older drugs which were often only effective against one or two types of parasites. Praziquantel is the only one of the current drugs that is not broad spectrum and it kills tapeworms which the other drugs are not effective against unless you use pyrantel at twice the normal dose.

But, these drugs are not all as effective as they used to be because they have been over-used and mis-used for many years. Now we have parasites that are becoming and have become resistant to these drugs so we have to change our deworming strategies to help slow the build up of resistance while still minimizing the parasite load in our horses.

It's now known that all adult horses living in the same situation do not necessarily need to be dewormed on the same schedule. 50% of horses in a herd will control parasite loads on their own due to natural resistance. Only about 20-30% of horses carry heavy parasite loads.
Thus each horse should be dewormed based upon an understanding of his own personal resistance to parasites. The best recommendation is now 2-4 dewormings a year based upon knowing which horses carry lots of parasites and which tend to carry little parasite load.

Rotational deworming is no longer an adequate or appropriate deworming program for adult horses. There are too many issues with strongyles developing resistance to 2 of the 4 most commonly used dewormers on the market---fenbendazole (more than 90% of areas tested have resistant strongyles) and pyrantel (around 1/2 of areas tested have strongyles resistant to this drug). And resistance is starting to be seen in strongyles to ivermectin---1st study showing it was done in KY in the last couple of years.

All adult horses in the continental US/Canada should be dewormed spring and fall with ivermectin/praziquantel or moxidectin/praziquantel. Other than those 2 standard dewormings, the rest of the deworming program should be based upon location and the horse's own resistance to parasites. The new recommendation is 2-4 dewormings per year based upon fecal egg counts used to determine the normal amount of egg shedding each horse does during the time of year when the weather in your area is most conducive to strongyle larva development and environmental survival. In the northern states in the US and in Canada, this means running a fecal egg count in the middle of summer (3 months after spring dosing if you used ivermectin or 4 months after spring dosing if you used ivermectin). In the southern US and Mexico you would be looking at testing in the middle of the winter (same time after spring deworming as listed above). Then based upon the number of eggs per gram of feces you can determine if you need more than the spring/fall dewormings and if so if you need 1 or 2 more dosings.

In the northern US and Canada, deworming should be discontinued during the winter months because the environmental conditions are not conducive to reinfection---that time of year has been proven to have extremely low reinfection rates. In the southern US and Mexico the opposit is true....deworming can be discontinued during the heat of summer because temps over 85 degrees lead to the infective strongyle larva dying quickly in the environment so the reinfection rates are lowest then.

For more detailed information check out the deworming webinar that was aired via The Horse magazine's website in April. Be prepared to sit for a while because it is an hour long presentation, but it's well worth the time. The veterinarian gives you all the information on strongyles and deworming in adult horses that you've always wanted to know and then some. It is a wonderful lecture. (And have plenty of paper and a pen.)…
(Craig R. Reinemeyer, DVM PhD --parasitologist)

WSArabians 11-03-2009 08:43 PM

Well, Ryle answered it!
Usually every 2-3 months, and certain dewormers work better during certain seasons due the type of worms they take care of and the type of worm that's out during either spring or winter.
Trimming/Deworming at the same time is the best way to remember, and I usually change it everytime I deworm to not build up a resistance.

Ryle 11-03-2009 08:50 PM

But there is no reason to deworm most horses every 8 weeks and certainly not every 8 weeks year-round.

Deworming 2-4 times a year period for adult horses in the US is the most current recommendation. For 50% of horses, twice a year is sufficient.

I deworm my 3 adult horses twice a year and my one senior horse 4 times a year. I do not deworm during the summer because the weather in my area is not conducive to parasite reinfection during that time of the year.

In the northern half of the country, summer is the time to focus on parasite control and winter is the time when the weather and living conditions control parasites for you.

Britt 11-03-2009 09:22 PM

I deworm 3 times a year with different dewormers that are targeted towards what types of worms and pests are more active for that time of year.

Equina 11-04-2009 02:58 AM

I had the same problem when I first bought my horse! The mysteries of deworming!

Ryle had some amazing info for you, plus google around a bit. And ask your vet. A big factor on when to deworm and with what product depends on your geographic location. One of my local vets even had a recommended deworming schedule on their website!

I deworm 4x per year. March is one of the -azoles. June is Ivermectin. October is Pyrantel Pamoate (this one needs to be done a couple weeks after the weather starts to freeze--when the buggers in your horse's feces are frozen dead, then you chemically kill the ones in his system, then you're hopefully all clear for a while). December is Ivermectin plus Praziquantel (gotta get those tapeworms, which only Praziquantel can do!) I live in a mild, northern coastal area, so my spring (June) and fall (Dec) (when Ryle recommendeds Ivermectin treatment) come a little later in the year than say...North Dakota.

Pasture management & the other horses also play a big role in parasite control. Sounds like you're at a boarding facility. If they pick out paddocks and haul-out the muck pile by truck to disposal, then you'll be much less likely to develop a parasite problem and could go with less deworming treatments per year. Also, if all the other boarders are accurately deworming their horses, then parasites are less likely to develop in their horses and spread to your horse. (This is probably why your old barn did dewormings for everyone.)

stacieandtheboys 11-04-2009 06:58 AM


Originally Posted by WSArabians (Post 449421)
Trimming/Deworming at the same time is the best way to remember, and I usually change it everytime I deworm to not build up a resistance.

I do this and it works great!

Ryle 11-04-2009 09:25 AM


Originally Posted by Equina (Post 449665)
Ideworm 4x per year. March is one of the -azoles.

You understand that based upon more than 10 years of research your deworming with a benzimendazole is very likely not doing a good job? Fenbendazole is the most commonly used benzimendazole and strongyles are resistant to it in 95% of the areas in the US that have been studied. Very few of the deworming products on the market in the US contain a different benzimendazole and even the others have resistance issues.

These products really shouldn't be used in a deworming program for adult horses unless you have tested for parasite resistance to them by running fecal egg counts prior to deworming and then again 10-12 days after deworming to ensure that you are getting a 90%+ reduction in the numbers of parasite eggs being shed.

As for the "treat for parasites that are active", other than treating in spring and fall with an ivermectin/praziquantel or moxidectin/praziquantel product to treat bots and tapes there isn't really an difference in what you are treating at different times of the year. Strongyles are the main concern all year round for adult horses.

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