Sorting Out Deworming Products

All of a sudden, it seems there are more new equine dewormers on the market than anyone can keep track of. What are these products? How should they be used? How are they different from those that have been on the market for a while? Which one is best for your horse?

Probably the first decision an owner must make is whether to deworm continually or periodically. Strongid C is an example of a daily dewormer. This alfalfa-based pelleted product can be added to the horse’s ration (recommended rate is 1 ounce per 250 pounds body weight) so that, theoretically, there is no chance for a parasite population to become established. To make its use more convenient, Strongid C can be added to a bulk mix at the rate of 25 pounds per 1,975 pounds of feed. Continuex is a similar product designed for daily use. Dosage is 1/2 ounce per 250 pounds of live weight. Both Strongid C and Continuex are labeled for use in stallions, young horses eating grain on a regular basis, and pregnant, lactating, or barren mares.

The active ingredient is pyrantel tartrate, an anthelmintic that is effective against strongyles, pinworms, and ascarids. Neither product eliminates bot larvae or tapeworms.

Deworming with an oral paste or gel is the option for those wanting to treat their horses on a periodic basis. Many products are available, and suggested usage schedules vary among the different types and brand names. While most products are safe for all horses, it is important to note label instructions that may warn against using a particular dewormer for a certain class of equine (for instance, extremely young foals).

A fairly recent development is the wide array of dewormers containing ivermectin, a chemical that has good effectiveness against many equine parasites including bots, but provides no protection against tapeworms. Several years ago the choice of ivermectin products was fairly small, but many brands are now available. Zimecterin, Equimectrin, and Rotectin 1 are examples. As long as the ivermectin concentration is the same (usually 1.87%), different products deliver the same protection to the horse, so purchasing an ivermectin dewormer should be done on the basis of cost, availability, and ease of use.

Products that list fenbendazole, oxybendazole, or pyrantel pamoate among their ingredients control the major equine parasites with the exception of bots and tapeworms. Safe-Guard, Anthelcide EQ, and Rotectin 2 are examples. Many people use a deworming schedule that rotates among the different chemical classes, feeling that this practice slows the development of drug-resistant parasites.

Quest, an oral gel dewormer, contains 2% moxidectin as an active ingredient. Quest controls many of the common equine parasites including bots as well as small strongyles in the encysted stage. It does not kill tapeworms. Labeled for use in mares, stallions, and foals older than four months, Quest is designed to be administered at three-month intervals, while many of the other paste or gel dewormers are given somewhat more often (every 60 days is a frequently suggested interval).

Several dewormers introduced to the market this year offer a combination of chemicals to control more parasites with a single product. Zimecterin Gold and Equimax combine ivermectin with praziquantel, a drug used to control tapeworms in cats and dogs. Another “all in one” product is Quest Plus, a mixture of moxidectin and praziquantel. Quest Plus is available only through veterinarians. Each of these products is effective against bots and tapeworms as well as strongyles, pinworms, ascarids, and a host of other equine parasites.

Ascarids, pinworms, threadworms, strongyles, hairworms, stomach worms, roundworms, cyathostomes, bots, tapeworms—horses harbor an array of parasites, and there are multiple names for some of the most common critters and their various life stages. It’s safe to say that all of these are potentially harmful to your horse, but why have tapeworms suddenly been singled out for special attention? For years, it was acknowledged that horses harbored tapeworms, but this type of worm was thought to be present in small numbers and was not considered particularly harmful. Maybe this belief was incorrect, or possibly tapeworms have moved in to fill the niche created as more effective deworming schedules eliminated many of the other parasites that used to crowd out tapeworms in the equine digestive tract.

In any case, the recent war on tapeworms has been justified by research linking them to colic, particularly the type caused by intussusception. This condition occurs when a section of the bowel telescopes into an adjacent portion, causing blockage, inflammation, and abdominal pain. Other studies have found that tapeworms are capable of secreting substances that interfere with the nerve impulses controlling peristalsis, the wavelike intestinal contractions that push food through the digestive system. As research continues, the message to the horse owner is clear: your horse’s chances of staying healthy are better if tapeworms are eliminated.

What deworming schedule should you adopt to give your equines the best protection against parasites? Which product is best for your horse? The answer, which varies by region, climate, pasture characteristics, and management procedures, is somewhat different for each owner. Are you in an area with warm weather all year long, or does a long and bitterly cold winter season put a seasonal end to bot exposure? Does your horse stay in the stall when he’s not being ridden, or is he turned out in a small paddock where decades of horses have grazed? Do you deworm all horses on a regular basis regardless of signs of parasite infestation, or treat only the horses that seem pot-bellied and rough-coated? Are your pastures drug or harrowed regularly to break up and spread manure piles, eliminating some parasite eggs by exposing them to weathering?

Answering these questions and discussing them with your veterinarian will help you choose appropriate products and intervals for a deworming program.

Kentucky Equine Research has not tested, and does not endorse, any particular brand or type of equine deworming product. Parasite control includes use of deworming products as well as other management procedures. Ask your veterinarian to help you set up a schedule and choose products appropriate for your region.