Two common nematodes that affect young horses are cyathostomes (small
strongyles) and Parascaris equorum (ascarids). It has been recently found that
populations of these nematodes are resistant to common anthelmintics used to control
them. Small strongyles have been found to be resistant to pyrantel and fenbendazole,
while ascarids have been found to be resistant to ivermectin. This represents a unique
dilemma in controlling the gastrointestinal nematode population in the foal. It has been
shown in other host species that combination anthelmintics can be used to successfully
treat resistant nematodes. The current study utilized 28 foals and was conducted from
April to November 2007. The foals were allocated into age cohorts and randomly
assigned a treatment regimen. Group I was administered ivermectin at 0.2 mg/kg BW.
Group II was administered ivermectin at 0.2-mg/kg BW and pyrantel pamoate at 6.6
mg/kg BW. Group III was administered ivermectin at 0.2-mg/kg BW and fenbendazole
at 10 mg/kg BW. Group IV was administered pyrantel pamoate at 6.6 mg/kg BW and
fenbendazole at 10 mg/kg BW. Fecal samples were collected at time of treatment and
two wk post treatment to determine effectiveness in removing egg producing adult nematodes. Each age cohort was then treated 30 d later with a different anthelmintic or
combination. That is, foals in group I were treated as those in group II, group II to
treatment III, group III to treatment IV, and group IV to treatment I. Over a period of 4
mo, each foal received at least one treatment in consecutive order.
The difference of egg counts (pre-treatment minus post-treatment) for small
strongyles treated with ivermectin (IVM) was 29.39 eggs per g (EPG), 5.44 EPG for
ivermectin with pyrantel (PRT), 3.85 EPG for ivermectin with fenbendazole (FBZ), and
-8.32 EPG for pyrantel with fenbendazole. There was a significant difference when
comparing IVM to IVM PRT (P = 0.0018), IVM vs. IVM FBZ (P = 0.0010), and IVM
vs. PRT FBZ (P < 0.0001). IVM was more effective than each of the other treatments.
There was no influence of treatment on ascarid EPG (P > 0.1184).
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2008-08-34 |
| Date | 16 January 2010 |
| Creators | Volker, Ashley |
| Contributors | Vogelsang, Martha M. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis |
| Format | application/pdf |
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