# Worming in hot weather



## Ryle (Jul 13, 2007)

If deworming in hot weather always caused colic we would see alot more of it in Texas.  While deworming can cause colic, it not commonly seen. Risk is higher if you are using a Panacur Powerpac (dosing fenbendazole at twice the normal dose for 5 days). 

However, if your temperatures are routinely over 85 degrees then deworming really isn't likely to be necessary because the environmental conditions are such that parasite larval contamination is going to be decreased and reinfection rates of horses is going to be low.


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## mls (Nov 28, 2006)

Ryle said:


> However, if your temperatures are routinely over 85 degrees then deworming really isn't likely to be necessary because the environmental conditions are such that parasite larval contamination is going to be decreased and reinfection rates of horses is going to be low.


 
Rather an ambiguous statement.


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## newhorsemom (Jun 20, 2008)

Thanks for the replies! I won't worry too much about making my horse sick nor will I worry too much if I'm a week or so late in worming!!

Thanks again!


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## Ryle (Jul 13, 2007)

Environmental conditions where the temperature is routinely over 85 degrees leads to much shorter larval survival on pastures. Which means that larval contamination of pastures is going to much lower. In the southern US where temps are over 85 degrees for extended periods during the summer months, the reinfection rates are the lowest of the whole year. Couple that with the fact that 50% of horses control parasite infections well through developed resistance and you end up nature preventing heavy parasite infections. 

Granted, this is not the case with foals who are susceptible to ascarids which aren't affected by environmental conditions.


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## nldiaz66 (Jul 27, 2008)

so Ryle: what you are saying if the temps are above 85 for the whole summer like down here in Florida,we dont have to worm as often as normal like every other month like I usually do ??


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## 7Ponies (May 21, 2009)

Yes, that's what she is saying.

There is an entire new worming protocol on the horizon. The old way of "worming every other month" is actually doing more harm than good as many strongyles are developing resistance to the wormers.

If you live in an area where your pasture heats up to above 85 degrees, it effectively kills the parasite eggs. I'm in South Carolina, and our pasture gets so hot in the daytime you literally can burn your feet in the sandy ground.

The same does not hold true for winter/frost. It will not kill the eggs. In fact, if you have a horse winter grazing and it can dig down to the grass and eat, it can become infected with strongyles even in sub-zero temps.

Do some googling about the new protocols. Interesting stuff.


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## nldiaz66 (Jul 27, 2008)

oh ok thanks, I've heard that you didnt need to worm every other month but never researched it.


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## toadflax (Jul 14, 2009)

Ryle said:


> Environmental conditions where the temperature is routinely over 85 degrees leads to much shorter larval survival on pastures. Which means that larval contamination of pastures is going to much lower. In the southern US where temps are over 85 degrees for extended periods during the summer months, the reinfection rates are the lowest of the whole year. Couple that with the fact that 50% of horses control parasite infections well through developed resistance and you end up nature preventing heavy parasite infections.
> 
> Granted, this is not the case with foals who are susceptible to ascarids which aren't affected by environmental conditions.



Ryle, what excellent information! I was reading a thread of yours on a different forum, it's really interesting, especially as I've been religiously following the every other month guidelines for years. 

I didn't quite understand how to implement the rotational worming you described. I'll be deworming with Panacur in a day or so--should I ideally be worming with Panacur again in 4 weeks? And how long till I worm again, and with what? Is this all determined by what an fec turns up?
Sorry to be dense about this, but I am really fascinated.
Do you have any links to share? Most of what my efforts turned up were the old news deworming schedules.


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## Ryle (Jul 13, 2007)

toadflax,
First, you should probably just drop fenbendazole (Panacur) out of your deworming regimen. In 90+% of areas tested worldwide, strongyles are resistant to fenbendazole (and the other benzimendazoles) so it's really not worth having in a deworming program for adult horses. 

If you are in the southern US, you shouldn't be deworming right now at all. If you are in the northeastern US, then you should have dewormed in spring with an ivermectin/praziquantel or moxidectin praziquantel and take a few month off from deworming and then collect a fecal sample. If you used ivermectin for your spring deworming, you need to not deworm again and take a fecal sample 3 months later or if it was moxidectin you would wait 4 months with no deworming and collect a fecal sample. Then have a FECAL EGG COUNT (that's important, you need a count and not just a fecal floatation) done and see how many parasite ova your horse is shedding per gram of feces. Then you use that result to determine if your horse needs to be dewormed more than twice a year and if so does he need to be dewormed 3 or 4 times. 


Here is updated information and a good link but have at least an hour set aside to watch the webinar:

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 www.thehorse.com. 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.  

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.) http://www.thehorse.com/Video.aspx?vID=1…
(Craig R. Reinemeyer, DVM PhD --parasitologist)


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## toadflax (Jul 14, 2009)

This is awesome!! (Who knew I could get so excited about, um, worms..?)
Thanks SO much for all the detailed information, Cindy. I will check everything out and share it with my boarder as well. 
We wormed with ivermectin about two months ago, so I guess it's fec time.


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## riccil0ve (Mar 28, 2009)

Ryle -- What if you don't do fecal egg counts? I've had my horse for two years, she gets wormed every three months, as was recommended by my vet. I don't have a schedule, I just grab something different every time. She is happy, and healthy. My almost-yearling filly has been getting wormed every month, as was also recommended by my vet for her first year. She is due to be wormed on the 1st, and it has been very, very hot for the Puget Sound area. My older mare isn't due again until September, so I'm only concerned about my filly. Should I not worm her? I can't recall what she was wormed with last, but she only gets part of a tube, and so she will be getting the last of the same stuff. What are your thoughts on this, Ryle?


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