Critical tests of a resin-pellet formulation of dichlorvos against internal parasites of the horse
Drudge, J.H.; Lyons, E.T.
American Journal of Veterinary Research 33(7): 1365-1375
1972
ISSN/ISBN: 0002-9645 PMID: 5039510 Document Number: 48393
In the USA, dichlorvos formulation -4 (Equigard Equine Anthelmintic), a resin-pelleted slow-release preparation was administered to naturally infected horses at various doses in feed and through a stomach tube. The drug affected the palatability of the feed and acceptance of the medicated grain was variable. Administration by stomach tube was not found to be satisfactory. The large volume of water necessary to flush the pellets down was thought to interfere with the action of the drug in the stomach. Single doses of 33 to 43 mg dichlorvos/kg body-weight were 90 to 100% effective against Gasterophilus intestinalis, G. nasalis, Parascaris equorum, Strongylus vulgaris, small strongles, Oxyuris equi and Probstmayria vivipara, and 65 to 75% effective against S. edentatus, provided S. edentatus, provided water consumption was restricted. Adverse effects were rarely observed, although a marked, but transient, decrease in plasma cholinesterase activity was noted in treated horses. Dichlorvos treatments at 8-week intervals did not adversely affect the pregnancy or fertility of breeding stock.