With drug-resistant parasites becoming an increasing problem in equine populations the veterinary community is currently struggling with new protocols with which to battle the squirmy little buggers that plague our horses’ innards.

My veterinarian is recommending a program that includes using the same class of de-worming drug for an entire year with several fecal examinations to determine actual numbers of eggs per microscope field. The goal of the new program is to get the egg numbers down to a set number per field but not down to a zero count. Attempting to get egg populations down to zero has been one of the main causes of the resistance – the other is the use of revolving drugs.

Since horses graze where they defecate it has been proven impossible to eliminate all parasites from the soil. Attempting to eliminate all parasites from our horses sounds like a sensible idea but has in fact created “super parasites” – able to leap tall horses with a single bound and stronger and smarter than those that have come before.

The rotating drug class method has created a situation much like what happens when patients do not take all of the antibiotic pills that their doctors have prescribed. The weaker bacteria are killed off sooner than the stronger so stopping the antibiotic therapy too soon leads to stronger and stronger bacteria left in our bodies and subsequently the environment. Administering a different class of de-wormer each time you worm your horse creates the same leftover super parasites. Ivermectin is great for some types of parasites but not others; panacur is better for others. Each time you de-worm with one and switch to another for the next round you only eliminate the weakest parasites that each drug was designed to target – of course leaving the strongest to reproduce even more of the strongest squigglies.

The other consideration, that being the lofty goal of zero egg counts, has created a host of adult parasites that produce eggs less often which then masks the adults’ presence. When fecal exams are run eggs are what is observed and counted under the microscope. If the adults are not producing eggs then the low or zero counts are falsifying the actual parasitic load within the body of the horse. This is where the danger lurks. Adult parasites not only attach themselves to the intestinal wall but also migrate into muscles and organs, including but not limited to the heart, lungs and corneas, causing all sorts of irreparable damage.

The bottom line – please touch base with your veterinarian to ensure that your de-worming program is current and effective. Together we will win the battle against the villainous super parasites and their nasty little offspring.