Since publication of last Spring’s newsletter article “New Deworming Recommendations: Resistance on the Rise”, there has been tremendous response and interest in alternatives to the “old” way of deworming. There has also been a lot of confusion on when to deworm, what dewormer to use, and the frequency of fecal exams. The simple answer to when to treat is to base treatment on fecal exams. A fecal exam that has nominal to no parasite eggs, per gram of feces, means that horse needs no treatment. Horses that have high numbers of eggs per gram of feces will obliviously need treatment. The one exception to this rule is deworming in the spring and fall regardless of a negative fecal to purge the horse of possible infection by bot flies.
The question of the type of dewormer to use should also be based on the fecal exam, the time of year and by the type of dewormer used to treat the horse the last time.
The frequency of fecal exams needs to be based on length of effectiveness of the last dewormer used, the risk of exposure the horse has to being re-infected by parasites and again the time of year.
For example: It is October, the first hard freeze has occurred, the horse has not been on pasture, the last fecal test was done two months ago, there was less than 150 eggs per gram of feces (EPG), and no treatment was recommended at that time. The recommendation now would to be deworm with an ivermectin product without a fecal exam. This recommendation is based on other parasites that can infect a horse during the year that can’t be detected by fecal exam i.e. bot flies. Another example: It is August, your horse has been on pasture, and the last deworming was in May with a fenbendazole product with a known efficacy of 8 weeks. The recommendation would be to perform a fecal exam and base deworming on the results. One more example: It is June, prior to turning your horse out on pasture part time; the last deworming was in May with a moxidectin product with a known efficacy of 12 weeks. The recommendation is not to perform a fecal exam or to treat due to the fact that the last dewormer is still excerpting its effectiveness.
We have performed numerous fecal exams at EMS since the spring newsletter was published and distributed. The majority of the exams have been either negative or well below the cut-off necessary to warrant treatment. Those horses did not have to be treated. There have been a few that were found to be heavily burdened with parasites that needed immediate treatment. In addition to the tests for internal parasites, we also test for sand when doing fecal exams at EMS. In doing so, we have identified several horses that have significant sand accumulations that were readily treated with Assure and Assure Plus.