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Discussion on Fenbendazole dewormer for non pastured horse in Phoenix, AZ
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New Member:
jones
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Posted on Tuesday, Oct 13, 2009 - 7:26 pm:
DrO,
I want to start using your recommended deworming schedule but I am a little confused about the recommendation to use a 5 day fenbendazole dewormer
(or equal "azole" option)
This drug is listed as part of the yearly rotation in your "Deworming Schedule for Horses" article and in your "Overview of Deworming Horses" article you seem to question its use/efficacy/possible damage to the intestines.
Is a 5 day moxidectin treatment preferable? or indicated?
I & my horse live in Phoenix, Az. My vet recommended giving a "powerpac" to my horse after he coliced 2 weeks ago. He is never on pasture and is in a dry turn out with one other horse in my back yard where I muck 2 times a day. They are on the same deworming schedule. They had been in a boarding facility for 2 months to get out of the summer heat and there he was turned out into a dry paddock only with his buddy as well. (They cleaned it out between each horse use!)
I have had him 3 years and do not know his previous worming history. I have rotated his dewormers the last 3 years on an every 3 month schedule, but I have never given him a 5 day treatment of anything. He had never coliced prior to this incident and had just, 2 weeks prior, returned back from the other boarding facility.
Also, I don’t know what a bot fly is (lucky me!)as in I never see them or their eggs and suspect they are smart enough to stay away from Phoenix.
If he is never on pasture & I do not have bot flies do I need to worry about tape worms & bots?
Do the deworming schedule season suggestions (ie winter drug choice vs summer drug choice)
remain the same for the desert when the temps are almost never below 50 degrees and the horse is never on pasture (my poor guy ;)
Regarding the possible reasons for the colic. He of course gets psyllium and probiotics 2 times a week for sand & he also gets ground flaxseed.
Thank you,
Lesley
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Moderator:
DrO
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Posted on Wednesday, Oct 14, 2009 - 8:55 am:
Welcome Leslie,
To answer your first question, "If fecal tests indicate you need to be on a regular deworming program the no you should not substitute an ivermectin for the fenbendazole routine." This defeats the one of the goals of this program. This is to avoid ascarid (round and pinworms) resistance by overexposing the parasites to the avermectin class of dewormers.
It should be noted this is not just any benzimidazole option but a specific product at a specific recommended (high) dosage for a specific time interval. This regimen has been highly researched for efficacy and toxicity and has been found to better reduce larval strongyle populations than even moxidectin. I have found that it is the only treatment that works on a local resistant ascarid population.
I do not see a fecal test result in your post. As explained in the Overview article Leslie it is critical you base your deworming program on the basis of fecal testing results and a discussion with your veterinarian with what parasites are indigenous to your area. You are in a bit of a specialized environmental zone and your local professionals will know best what is best.
Other than the initial burden the horse may have had when he came to you, if your horse cannot be exposed to a particular parasite there is no reason to be concerned about that particular parasite. You can read more about the life cycle of all the intestinal parasites at Diseases of Horses » Colic, Diarrhea, GI Tract » Parasites and Worms. Depending on how often the paddocks are cleaned there may be other parasites that you do not have to be concerned about.
DrO
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New Member:
jones
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Posted on Wednesday, Oct 14, 2009 - 10:08 am:
DrO,
Thank you! I have not done a fecal count with him. If a fecal egg count is negative 90 days after the last dewormer was administered, when would it be wise to do the next fecal test given the significant possibility of a false negative test. I assume the test results indicate what kind of worms are laying the eggs?
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Moderator:
DrO
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Posted on Wednesday, Oct 14, 2009 - 12:57 pm:
Why would you consider such a test to be a false negative Lesley?
The Horse Care » Worms, Deworming, Parasite Control » Deworming Schedules has recommendations on frequency of fecal checks based on the rate of infection, I will check to be sure these recommendations are clear. Yes each family of worms and in some cases particular species have distinctive eggs, these are described in the parasite articles referenced above.
DrO
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Member:
jones
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Posted on Sunday, Dec 20, 2009 - 2:25 pm:
Dr. O.
Sorry for the delay...I have just really gotten to understand how to use this site 
Regarding the fecal tests and their validity,
Your article "general over view of deworming" mentions the weakness inherent in the test and my vet sldo stated fecals egg test have a risk of false negatives. I will do the test but want to know how often to repeat it if it comes out negative.
(I have a post under colic with you at the moment)
then regarding the Panacure...
Below is from the your article "Deworming Over view" In the second paragrap toward the end it suggests that panacure is not effective and harmful to the lining of the intestine. Read below.
The Benzimadazoles: Panacur, Anthelcide, Safe-Guard and many others
There is a large family of benzimidazoles and contain some of the most often available and most often used dewormers. Though it is impossible to list them all, look for the name of the active ingredient to end in "azole". Thiabendazole and fenbendazole probably have some of the worse resistance problems while oxibendazole and oxfendazole the least problems. Some of this group tend to be more toxic and (cambendazole) not suitable for pregnancy. All of this class of deworming pastes have little effect on the encysted larvae at the recommended one time dose and all have the potential for resistance problems making their use questionable in a good deworming program.
Recently a high dose five day (10 mg/kg for five consecutive days) treatment of Panacur (fenbendazole) has become available which will kill 90% of all the larval stages in the horse. This includes a good efficacy against the encysted dormant larvae. These have been difficult to kill with any other deworming product. They can be a cause of diarrhea, weight loss, and chronic colic. The treatment is expensive and really does not figure in well with well managed healthy horses. This may be useful for treating horses with signs of anthelmintic larval disease and horses with a poor history of parasite management before introducing them to a herd. In late 2003 one study showed the high five dose Panacur treatment having incomplete efficacy for killing egg laying adult strongyles, which calls into question whether this is as effective at killing encysted larvae as has been thought. In 2006 the use of the five day dose of Panacur vs Moxidectin were compared. While both did a good job of clearing encysted larvae there was far more inflammation and ulceration of the bowel associated with the use of Panacur. It was proposed that the Panacur killed L4 mimicked a larval eruption as seen in cyanthostominosis while the moxidectin tends to dissolve the worms resulting in less reaction.
I did the panacure but am unlikely to repeat it.
He came off his food on the 4th day of the panacure.
I should do a fecal egg test now? (60 days after the panacure?) (I have a post with you under Colic at the moment asking how to the best way to do a fecal test...I see kits in the valley vet catalog.
Thank you.
Lesley
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Moderator:
DrO
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Posted on Monday, Dec 21, 2009 - 7:26 am:
Hello Leslie,
Check out the topic Horse Care » Worms, Deworming, Parasite Control » Deforming Schedules it discusses this question including what to do with negatives.
Concerning the use of larvicidal dose of fenbendazole, these are the kinds of questions we had to tangle with coming up with these recommendations. It needs to noted that it was not the medication that was believed to cause the damage but the way it killed the larvae. There is damage in both cases, you cannot kill encysted larvae without some reaction. The question then becomes which is worse: the difference in the transient bowel inflammation or the development of ivermectin resistance in strongyles. Parasitologist feel strongly the avermectin problem is the most significant for if we loose the efficacy of this dewormer...
DrO
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