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Deworming Your Horse

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Historically, the most effect way to control parasites was believed to be by deworming every 8 weeks with a rotation of the class of active ingredient used. This approach has resulted in the development of resistant strains of parasites. Individual worms develop resistance to a particular drug due to random genetic mutation. Indiscriminate deworming kills off the competition and gives these worms an advantage for survival. The more frequently the horse is dewormed with the resistant chemical, the quicker the population of resistance worms increases.

The solution appears to be in strategic deworming. Egg counts in the manure are done and the horses that are heavy shedders are dewormed and those that are light shedders are not dewormed at that time. Confirmation that the treatment worked is produced by completing a second egg count 10-14 days after treatment. This selective deworming will not eliminate resistance but will slow it down.

Work with your veterinarian to perform egg counts on your horses and identify the level of shedding of each horse. The vet can then recommend a treatment and determine effectiveness by egg counts after said treatment.

There are some management procedures that you can do to help control the parasite load in your horses.

1.  Allow at least two acres of pasture per horse. This will give horses enough room to establish “toileting” areas, which they naturally avoid when grazing.

2.   If available, periodically rotate horses to another pasture for at least a year at a time, this allows parasitic eggs and larvae to mature and die off from environmental exposure in the rested pasture.

3.  Pick up manure in pasture spaces at least weekly.

4.  Compost manure before spreading on fields.  Use horse manure on fields used for feed for cattle, not for horses.

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