This is an archived Horseadvice.com Discussion. The parent article and menus are available on the navigation menu below:
HorseAdvice.com » Treatments and Medications for Horses » Dewormers (Anthelminics) » Quest (moxidectin) »
  Discussion on Fenbendazole vs moxidectin
Author Message
Member:
lynnland

Posted on Saturday, Dec 12, 2009 - 9:04 am:

Hi Dr. O,

I have read the info on parasites and associated drugs used to control them but am still a little confused as to why you would use a 5 day Panacur double dose for encysted small strongyles when it appears the 1 day single dose moxidectin will do the trick. I am sure this has been asked before but I cannot seem to find it anywhere.

Thanks again

Lynn
Moderator:
DrO

Posted on Saturday, Dec 12, 2009 - 10:06 am:

Hello Lynn,
The growing dependence on the avermectin class (ivermectin and moxidectin) of anthelmintics is resulting in decreasing prepatency periods for small strongyles. This is the first sign of resistance. Also there have been reports of resistance of ascarids (roundworm and pinworms) to avermectins.

Though I had read about this for several years I had found a successful management using just moxidectin, ivermectin, and pyrantel dewormers. Then I had a farm that came up with a case of ascarid resistance to avermectins. Then I decided it was time to include a benzimadazole class and the power pack is the only treatment regimen that really is effective against the larvae and seems to even treat benzinadazole resistant ones.

More details on this and other aspects of developing a effective program are provided at Horse Care » Worms, Deworming, Parasite Control » Overview of Deworming.
DrO
Member:
lynnland

Posted on Sunday, Dec 13, 2009 - 8:40 am:

Thanks much Dr. O.

Lynn
Member:
npo33901

Posted on Monday, Dec 21, 2009 - 4:26 am:

Lynn, how do you know that it is encycted strongyles ?
How does it look like ? Could you take a picture/description , please ?
Member:
lynnland

Posted on Monday, Dec 21, 2009 - 7:36 am:

Hi Anna-Marie,

I am actually taking a shot in the dark here. I have a horse with intermittent mild diarrhea and stomach/intestinal discomfort. I actually posted a whole history under stomach ulcers (see: HorseAdvice.com » Diseases of Horses » Colic, Diarrhea, GI Tract » Gastric Ulcers » Gastric Ulcers in Adult Horses » Sucralfate - treatment duration). The horse carries good weight and is nice and shiny so worms is not what comes to mind. However, I don't have lots of information on his worming history and the treatment is very unlikely to do any harm so...I gave it a try. Just finished the last treatment yesterday so I will give him 2 weeks before trying something else.

Cheers

Lynn
Member:
lynnland

Posted on Monday, Dec 21, 2009 - 8:32 am:

Hi Dr. O,

How long does it normally take for the 5-day fenbendazole treatment to take effect? Do the encysted larvae become affected only in the last few days of treatment then take a few more days to come out? Also wondering if there is any info on how long it might take the intestine to heal after the encysted larvae erupt.

thanks

Lynn
Moderator:
DrO

Posted on Tuesday, Dec 22, 2009 - 7:04 am:

This is not well studied and the information we have comes from just a single source, here is a summary of their findings:
DrO

Vet Parasitol. 2006 Jun 30;139(1-3):115-31.
Small strongyle infection: consequences of larvicidal treatment of horses with fenbendazole and moxidectin.
Steinbach T, Bauer C, Sasse H, Baumgärtner W, Rey-Moreno C, Hermosilla C, Damriyasa IM, Zahner H.

Institute of Parasitology, Justus Liebig University Giessen, Rudolf-Buchheim-Strasse 2, D-35392 Giessen, Germany.

The study was undertaken to evaluate adverse effects of larvicidal treatment in horses naturally infected with cyathostomins. Out of 24 ponies kept on pasture, four animals were housed in September and anthelmintically cured to serve as worm-free controls (group C-0). The others were housed in December. Eight animals each were treated 8 weeks later with 5 x 7.5mg/kg fenbendazole (FBZ) or 1 x 0.4 mg/kg moxidectin (MOX). Four animals remained untreated (group C-i). Two, 4, 6 and 14 days after the end of treatment two animals of each of the treated groups were necropsied together with group C-0 and C-i animals. Infected animals before treatment showed weight loss, eosinophilia, increased plasma protein and globulin contents. Treatment was followed by weight gain and temporal plasma protein and globulin increase. Proportions of CD4+ and CD8+ T lymphocytes in the peripheral blood did not differ between the groups before treatment but DrOpped significantly temporally after FBZ treatment. Group C-0 was worm-free at necropsy. Group C-i animals contained variable numbers of luminal and tissue cyathostomins. Histological sections showed larval stages in the lamina propria und submucosa surrounded by macrophages. Either treatment was effective against luminal parasites and reduced the number of larvae in the bowel wall beginning 4-6 days after FBZ and 6-14 days after MOX treatment. Histologically, as a first reaction after FBZ application T lymphocytes accumulated around morphologically intact L4 in the submucosa. Subsequently T lymphocytes associated with eosinophils infiltrated the submucosa. Parasites became enclosed by granulomas with eosinophils adhering to and invading the larvae which started to disintegrate on day 4. Later on, particularly on day 14 inflammation extended into the mucosa and was frequently associated with ulcerations. Third stage larvae in general and L4 in the lamina propria, however, seemed not to be affected until day 14 and even then, parasites did usually not generate extensive inflammation. After MOX treatment severe morphologically detectable alterations of tissue larvae could not be observed earlier than day 14. Different from FBZ treatment, larvae disintegrated and were obviously resorbed without causing severe inflammation in the gut wall. In conclusion treatment with either drug was efficacious against tissue larvae of cyathostomins but there may be different clinical consequences: in contrast to MOX effects, killing of larvae due to FBZ was associated with severe tissue damage, which clinically may correspond to reactions caused by synchronous mass emergence of fourth stage larvae, i.e., may mimic larval cyathostominosis.
Member:
lynnland

Posted on Tuesday, Dec 22, 2009 - 7:37 am:

Thanks Dr. O,

It amazes me that there aren't more studies with respect to how long it takes for this to work. It looks like my horse had a mild colic event on day 5 of treatment; significant pawing in his stall that night, something he has never done before.

Thanks

Lynn
Moderator:
DrO

Posted on Tuesday, Dec 22, 2009 - 4:09 pm:

Using the information in the study above, if he had a remarkable L4 burden this may be related to the deworming however there is a good chance that this is coincidental: clinical problems with the regimen are uncommon.
DrO
Home Page | Top of Page | Join Us!
Horseadvice.com is a BBB Accredited Business. Click for the BBB Business Review of this Horse Training in Stokesdale NC