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Parasite Resistance and Strategic Deworming

If you are a long time horse owner, the traditional parasite control strategy has been to deworm your horse every 6-8 weeks year round, rotating products, or providing a daily dewormer in your horses feed, and deworming twice a year with a paste product. Years of constant deworming has contributed to the development of parasite resistance to many deworming products out there. With no new deworming products coming out on the market, it is vital that we practice judicious use of the products that are still available to us. It is now recommended to tailor your horses deworming protocol based off of fecal examination. In many horses the number of times you deworm your horse each year can be greatly reduced, saving you money on deworming and keeping your horse healthier.

The McMasters Fecal Egg Count is a simple test performed by your veterinarian to determine the parasite load present. This test involves identifying and counting different types of parasite eggs in a fecal sample by examining it microscopically. Results are reported in eggs per gram (EPG) of feces. In general, a low egg count (less than 200 EPG) indicates a low parasite burden, while a high egg count (500-1000 EPG, or greater) indicates a large number of parasites present. High fecal egg counts suggest ineffective deworming, a lot of parasites in the environment or parasite resistance. It is recommended to repeat fecal egg counts two weeks after deworming on all high and moderate egg count horses to determine the effectiveness of the deworming product used and to identify resistance to a particular product.

For some parasites, particularly Tapeworms, they only shed their eggs intermittently, so a low or negative fecal egg count does not necessarily mean the parasite isn’t in the environment. Deworming programs based off fecal egg counts still rely on some scheduled deworming to control these parasites. It is recommended to deworm your horse at least once a year with a product that contains Praziquantal. Examples are Zimectrin Gold or Quest Plus.

Deworming strategies should be based off of fecal egg counts, age of horse, time of year and exposure level (type of pasture, exposure to unfamiliar horses). Here in Florida, the summer months provide some parasite control. High temperatures (greater than 85° F for five conseutive days) kills parasite eggs on your pasture so there is little reinfection of parasites during the summer months. Consult with your veterinarina about performing fecal egg counts and developing a strategic deworming program. Please feel free to drop off a fecal sample at our office too. All we need is one fresh manure ball, in a ziploc baggie labeled with your name and horses name on it. Manure should be less than 12 hours old, and kept refridgerated until evaluation.

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