from the Vet Corner Archives

Part of Horse Previews Magazine website. Posted on 1/1/98; 10:00:00 AM.

Veterinary Corner 1/98: Quest (Moxidectin)

by Katherine Burnett, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069

Moxidectin has been marketed furiously as the new miracle dewormer for horses. In fact, it does have some unique properties that set it apart from other products and make it very useful in most deworming programs. It should be used cautiously, however, as it is not free of side effects.

Quest need not, and should not, be used any more often than every three months. It lasts longer than other dewormers because it is stored in the fat cells and released into the body slowly. Because it is fat soluble, it can also be absorbed into the brain tissue, and when overdosed can cause incoordination and other signs of nervous system toxicity. It is important to use a weight tape on your horse to estimate the proper dose before administration. If you have a pony or miniature horse, have your veterinarian estimate its weight before giving the product.

What sets Moxidectin apart from the other dewormers is that it kills encysted small blood worms in the large colon. These encysted worms are a leading cause of colic. There have been reports of severe colic and even death following administration of Moxidectin. This is probably not due to toxicity, but instead to an inflammatory reaction to a large kill-off of worms. For this reason it is probably ill-advised to give this product to debilitated horses or to those who may not have been on a good deworming program prior to treatment. Additionally, foals under four months of age should not be dewormed with Moxidectin, and it should not be used for a foal's first deworming.

Despite what the ads say, Moxidectin does not kill all species of worms - no product does. For this reason, rotation is still advised. Contact your veterinarian for specifics.

Horse Previews and staff would like to thank Dr. Burnett for writing such interesting articles these past months, and wish her all the very best of luck in her new venture in California. Look out for continuing vet articles next month by a new author!

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