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Parasite control options

Jeremy D. Frederick, DVM, University of Minnesota

A comprehensive parasite control program involves more than deworming your horse on a regular basis. The most important feature is the ability to reduce the number of parasites and eggs in the environment. Secondly, the program should be effective with the fewest number of treatments necessary. Finally, the program should be broad spectrum to control many different types of parasites.

Preventative medication is a very important component of parasite control. The bad news is that there is no single program that works for all situations. However, there are many different programs available, these include:

Targeted Dosing: This strategy involves testing the level of parasite burdens in individual animals. Standard fecal egg counts should be performed once monthly. Also tapeworm testing via fecal testing or serology (blood testing) should be done twice yearly. All animals that are positive over a certain cut off level should be treated. A yearly treatment for "bots" should also be included during the winter. This program is only appropriate for adult horses and should be considered on a farm with a dedicated manager where good grazing management is in place.

Strategic Dosing: This strategy involves treating all pastured animals at regular intervals with an appropriate product. The interval between dosing can be determined by the egg reappearance period (ERP)of the medication, which is shorter for young animals. The ERP is the period after medicating an animal with a dewormer until there are significant numbers of parasite eggs present again in the feces. The animals are only treated during the spring/summer season when the risk for increased egg loads is highest.

Interval Dosing: This strategy is the one most commonly used. It is similar to Strategic Dosing; however, animals are treated year round at regular intervals. As the duration of parasite kill varies from product to product and even between farms, the interval between doses should be determined by the ERPor by guidelines set by your veterinarian based upon products used. This program may be appropriate for farms where there are frequent new additions to the group, at more casually managed (hobby) farms and in young animals.

Daily Deworming: This strategy involves the addition of a parasite control medication to the horse's daily ration. This program is appropriate for most adult grazing horses; however, additional periodic deworming with other products is usually necessary. Twice yearly treatment with ivermectin (Eqvalan, Phoenectrin, Zimectrin), ivermectin/praziquantel (Equell) or moxidectin (Quest) has been recommended. This program can select somewhat for resistant organisms since the parasites are continuously exposed to a low level of the drug.

For more information, see Parasite control information.

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