Are you over-drugging your horse?

By: Dr. Niki Whitley, NCA&TSU CEP

When easy-to-use, effective horse dewormers were introduced, horse owners were advised to deworm all horses every 8 weeks and to rotate among dewormer classes.  This is a very common recommendation even today.  But is this 40-year-old practice still the best recommendation for horse owners?

Many horse owners are driven by fear when following deworming recommendations and drug companies probably feed into that fear.  However, according to equine parasite expert, Dr. Ray Kaplan, most adult horses will remain quite healthy with much fewer treatments than what is currently recommended (work with your veterinarian to determine your situation).

Why would this issue even come up if horse owners are happy giving the drugs and the horses are healthy?  Well, the same problem that plagues the sheep and goat industry (worm resistance to dewormers) has also been found in the horse industry. 

Resistance of small strongyles to benzimidazoles (Safeguard®, Panacur®, Anthlecide®, Benzelmin®, etc.) is well-known, occurring in over 21 countries, including the U.S.  Over 40% of farms tested in KY had worms that were resistant to benzimidazoles and pyrantel pamoate (such as in Strongid®, Exodus®, Rotectin®, etc.) and some farms showed reduced activity to ivermectin (perhaps an indication of the beginning of resistance).  Other worms have also started showing resistance.

In order to prevent dewormer resistance, many of the same internal parasite management recommendations can be made for horses as for sheep, goats and cattle. Managing pastures and stocking rates is important for all species. Multi-species grazing can help control worms (as long as the species don’t share worms; sheep/goats share worms with each other but not with horses and cattle).  One of the best methods to help control resistance to dewormers is to only treat those animals needing it. Don’t over-drug your horses.

How do you know if a horse needs to be dewormed?  In a population of mature animals, only a very few carry heavy worm burdens and they can really infect the pastures with worm eggs. Dr. Kaplan recommends working with your veterinarian, having fecal egg counts conducted to determine which animals have a problem and concentrate mostly on those animals, using a strategic deworming program.

More information is available from www.thehorse.com in a compilation of 12 articles on internal parasites of the horse called “Bad Bug Basics”.  Always consult your veterinarian if you have concerns about your horses. 

Source:  “Current concepts for parasite control in horses: It ain’t the 60’s anymore”, by Dr. Ray Kaplan (Proceedings of the 27^th Annual Alberta Horse Owners and Breeders Conference, January, 2009).