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Ectoparasites - Control

The problems resulting from parasite worry make control of external parasites essential. Horses that cannot eat or sleep do not thrive. Insecticides in a variety of preparations are used to kill both arachnids and insects. Dusts or powders may be applied to animals. Transmission will be kept to a minimum if horses are kept in clean dry quarters and if overcrowding is avoided. Frequent, thorough grooming will remove some parasites and will provide an opportunity to detect ectoparasite damage at early stages.

Elimination of external parasites from an area is difficult if the parasites involved are capable of living for prolonged periods off the host. Ticks, for example, can live in the environment for 200 to 300 days without feeding. Horses in areas where many ticks exist are continually reinfested. Treatment must therefore be repeated regularly. Furthermore, ticks are not completely species-specific. That is, although one kind of tick may prefer to feed on horses it may sometimes infest cattle or other animals, and they too must be treated in any attempt to reduce tick populations.

The control of ectoparasites has been practiced with mixed results over the last 60 years. Two classes of products are currently used against all the major equine ectoparasites, namely, the gamma isomer of benzene hexachloride (BHC) and the organophosphates, including diazinon and trichlorfon. BHC was introduced in the late 1940's, and the organophosphates in the 1950's. Both compound classes are applied as sprays, dips, pour-ons, dusts and washes.

Several disadvantages of the currently available products include the necessity for frequently repeated treatments in situations in which reinfestation occurs rapidly. The organophosphorus compounds are cholinesterase inhibitors and, as such, can be dangerous to horses if used incorrectly or if applied concomitantly with an anthelmintic that is also a cholinesterase inhibitor.

Power sprayer used to apply insecticides


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