A Field Study on the Effect of Some Anthelmintics on Cyathostomins of Horses in Sweden |
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Authors: | E Osterman Lind T Kuzmina A Uggla P J Waller J Höglund |
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Institution: | (1) Department of Parasitology (SWEPAR), Swedish University of Agricultural Sciences and National Veterinary Institute, Uppsala, Sweden;(2) Department of Parasitology I.I., Schmalhausen Institute of Zoology, Kiev, Ukraine |
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Abstract: | The objective of the study was to investigate different aspects on the efficacy of three anthelmintics on cyathostomin nematodes
of Swedish horses. A faecal egg count reduction (FECR) test was performed on 26 farms. Horses were treated orally with recommended
doses of ivermectin, pyrantel pamoate or fenbendazole. Faecal samples were collected on the day of deworming and 7, 14 and
21 days later. No resistance was shown against ivermectin; the FECR was constantly >99%. The effect of pyrantel was assessed
as equivocal in 6 farms 14 days after treatment; the mean FECR was 99%. As many as 72% of the fenbendazole-treated groups
met the criteria for resistance; the mean FECR was 86%, ranging from 56% to 100%. A re-investigation of two farms where pyrantel
resistance had been suspected clearly revealed unsatisfactory efficacy of pyrantel on one of these farms; the FECR varied
from 72% to 89%. Twenty-six of the horses previously dosed with pyrantel or fenbendazole, and which still excreted ≥150 eggs
per gram of faeces 14 days after treatment, were dewormed with ivermectin and fenbendazole or pyrantel in order to eliminate
the remaining cyathostomins. A total of 13 cyathostomin species were identified from horses that initially received fenbendazole
and seven species were identified from pyrantel-treated individuals. The egg reappearance period (ERP) following treatment
with ivermectin and pyrantel was investigated on two farms. The shortest ERP after ivermectin treatment was 8 weeks and after
pyrantel was 5 weeks. We conclude that no substantial reversion to benzimidazole susceptibility had taken place, although
these drugs have scarcely been used (<5%) in horses for the last 10 years. Pyrantel-resistant populations of cyathostomins
are present on Swedish horse farms, but the overall efficacy of pyrantel is still acceptable. |
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Keywords: | anthelmintic resistance cyathostomins egg reappearance period (ERP) faecal egg count reduction test (FECRT) horse |
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