It is common practice in all types of livestock to deworm at regular intervals, and this has been effective for a long time. However, resistance is developing to the deworming medications we now have and no new dewormers are being developed for the future. Resistance is so severe in goats and sheep that many areas cannot raise these animals anymore because the dewormers are ineffective and the worms kill the animals. Although the problem is not that severe in horses yet, it is believed it will be unless we change our thinking process and change our deworming protocols.

It is common for most horse people to deworm their horses every 2 to 3 months routinely. However, Dr. Cyprianna Swiderski from Mississippi State indicates all we are doing is killing the susceptible parasites and therefore are selecting for the resistant parasites. She indicates that only 25% of the horses account for 80% of the pasture contamination and these are the horses that need to be dewormed. Many horses have immunity to fight off the parasites without deworming and can limit the parasite life cycle without deworming medication. So the key is to determine which horses belong to the susceptible group and which horses are resistant to the parasites. And the best method of doing this is to ask your vet to perform fecal exams on all of your horses before you deworm them early in the parasite season. By identifying susceptible horses, you will know these horses need to be dewormed routinely and you can save your money and not have to deworm horses that are resistant to parasites. Talk to your vet about checking your horses for parasites rather than just deworming them every 2 to 3 months.