Horses are highly susceptible to internal parasites. Georgia has a warm, moist climate that promotes optimum survival of internal parasites. Many dewormers have been on the market for over 20 years and resistance to these drugs has developed. For many years it was recommended that horses be dewormed using a frequent rotation program with a different drug used every 60 days. In fact this program is now known to actually contribute to the development of resistance. At this time there are no new equine dewormers being developed. It has become essential for the horse owner to treat their horse for internal parasites only when needed to protect their horse and to minimize the development of resistance. We now recommend using a strategic deworming program using a McMaster’s fecal analysis as a guide.
In Georgia the most damaging parasites are the small Strongyles (Bloodworms). Small Strongyles are at peak activity in the fall. All horses should have a fecal sample tested in September – October. We look at the fecal egg count and group horses into one of 3 categories, Low, Medium and High. Horses with low fecal egg counts do not need deworming. These horses can be treated for bots and tapeworms in December after a hard killing frost and many only need a single treatment per year. Horses with moderate to high fecal egg counts should be dewormed. With a second treatment after a hard, killing frost for bots and tapeworms. A spring fecal test should be done in April. Most adult horses in Georgia do not need deworming during the summer months when temperatures are high and rainfall is low. By using an effective product at the time of most impact most adult horses can be dewormed 1-3 times a year and achieve excellent control.
Several years ago daily dewormers were very popular. A daily dewormer must be given every day in the proper amount. Horses which are fed in groups will swap feed buckets and not receive their proper dose. Horses that spill their feed may not consume their full dose. When horses do not receive their full dose each day it is inevitable that resistance will develop. After many years of testing horses who were colicking while on these products we no longer recommend them.
Once a horse has developed resistance to a drug you can no longer use that drug in that horse ever again.
Dewormers belong to 4 basic classes of drugs. Many different brand names are used to sell the same drug; for instance EquiMax, Equimectrin, Eqvalan, IverCare, Ivercide, Phoenectin, Rotectin 1, and Zimectrin are all the same drug, Ivermectin. This can be confusing to horse owners when selecting products for deworming. We encourage our horse owners to let us help you when selecting your horses’ deworming product.