Feed Through Fly Control Options

Veterinarians and drug companies agree that feed-through fly control for horses--along with proper land and stable management--can keep barn fly populations under control. Fly control management is a serious problem facing horse farms of all sizes.

There are two major categories for feed-through fly control products--those containing organophosphates and those that are organophosphate-free. Products with organophosphates contain the active ingredient tetrachlorvinphos (TCVP). Organophosphate products are formulated to maximally pass through the digestive system in the manure, with minimal absorption. Female house and stable flies then lay their eggs in manure deposited on the ground. These eggs will hatch into larvae, but will be prevented from growing into adult flies because the TCVP affects the larvae's nervous system. In fact, according to Anne Robertson, public relations director for Farnam Companies that manufactures some feed-through products (Equitrol), "TCVP inhibits cell and muscle cholinesterase activities in flies with consequent disruption of nervous system activity, which results in the insects' death."

TCVP is registered with the Environmental Protection Agency (EPA) for use in horses, swine, and beef and dairy cattle. It has been a registered product for more than 25 years as a feed-through oral larvacide for fly control in horses. Organophosphate products have been proven 99% effective against house and stable flies with a daily dosage of the supplement.

The other class of feed-through fly control is organophosphate-free, and can currently only be purchased through a veterinarian. This product works much the same, in that it passes through the digestive tract of a horse, with virtually no absorption. The active ingredient in this organophosphate-free product is the insect growth regulator (IGR) Cyromazine. According to Dennis French, DVM, Dipl. ABVP, of Louisiana State University, "Cyromazine works by inhibiting the synthesis of the exoskeleton (chitin) of the insects. In other words, it does not allow for the formation of the skeleton, and thereby inhibits the development of the eggs to larval and pupal stages."

Mike Coffee, president of Triad Specialties that manufactures this type of product (Serene), explained how this can be accomplished: "Cyromazine prohibits proteins from lining up correctly during development; therefore, the flies are unable to form their proper outer shells, or exoskeletons, while they are in their cocoons, and will be unable to hatch out into flies."

French added, "Cyromazine has very high insect specificity, against the fly families and then degrades into a nitrogen compound, melamine, after about 35 days on pasture acting much like a slow release fertilizer."

The EPA declared the Cyromazine feed-through fly control product as safe for use in horses in January of 2004. The organophosphate-free product has been proven to prevent 95% of immature stable flies and 100% of immature house flies from developing into adults. The Cyromazine feed-through fly control product is to be given to the horse as a topical feed supplement every other day.

"The reason the product is only issued through veterinarians is because the product takes approximately 4-6 weeks before it is recognizably working, and most consumers want immediate satisfaction," according to French. The product has the lowest EPA drug toxicity level, and it has been found to be safe for use in gestating and lactating mares and their foals.

It is suggested for use of all feed-through fly control products to begin administration of the supplements, in most areas, beginning in March before the fly season starts, and stopping around the end of October. However, in warmer, more humid areas, such as Texas and Florida, it is often suggested to begin feeding the product earlier, with veterinarian consultation. This is because no feed-through fly control supplements are effective against adult flies, but they can be instrumental in controlling reproduction of flies, and keeping them from overpopulating barns.

About the Author

Rachael C. Turner

Rachael Turner is the former Photo and Newsletter Editor for The Horse. She is an avid event rider. Rachael's main focus is dressage and on training young horses with the proper foundation for success. She is also a member of the United States Dressage Federation and the United States Equestrian Federation. Her website is avonleaequestrian.com.

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