How Feed-Throughs Work
Farnam's SimpliFly and Pfizer's Solitude IGR products are formulations that contain insect growth regulators. They keep the fly from developing into an adult. As such, the active ingredients (diflubenzuron in SimpliFly and cyromazine in Solitude IGR), specifically target insects. Plus, the products are able to use small amounts of the ingredients.
"Conventional insecticides have a direct toxic effect on the nervous system," Ross says. "That can also affect vertebrates such as you and me, horses, dogs, etc. Insect growth regulators disrupt the processes that are unique to insects. Because of that specificity, they're safer."
SimpliFly uses an ingredient that Ross says is also used in flea control products. "When the larvae molt, the chemical prevents it from making a new external skeleton or shell. So they never get to the adult stage." SimpliFly is fed by weight, usually 1 ounce daily for a 1,000-pound horse.
Cyromazine, the ingredient in Solitude IGR, was initially used to regulate flies around chickens. Kathy Palma, an entomologist with Triad Specialty/Piedmont Pharmaceuticals and also a barrel racer, knew of cyromazine through her work and tried it on her horses.
"The active ingredient looks like salt," Palma says, "so I took a pinch to see what it would do. Four or five weeks later, there weren't that many flies."
Palma and a scientist friend began running tests on the manure, which confirmed her results. While Solitude IGR is a new product, Palma says she has been using cyromazine on her horses for five years without any complications.
Donecker says that because cyromazine is water soluble, it's not easily absorbed in the body and passes through a horse's intestinal tract and into the manure. "Sunlight breaks it down," he says. "It breaks down into nitrogenous compounds, some of which have been used for fertilizer."
Donecker says that Solitude IGR is fed either daily (½ ounce) or every other day (1 ounce).
The Environmental Protection Agency regulates the ingredients found in both SimpliFly and Solitude IGR. Products such as these must pass tests for both effectiveness and safety. As with any fly control product, you should check the label for indications for young, pregnant, aged, or infirm horses, as well as consult with your veterinarian.
Some previous feed-through fly control products contained organophosphates, which targeted an insect's nervous system. However, a study by a team of researchers at U.C. Davis led by Dr. John E. Madigan, showed that horses absorbed organophosphates, which could affect their nervous systems as well.
"Feeding horses organophosphates, which are absorbed, seems to be a poor way to control flies," Madigan said. "It makes much more sense to use a metabolic interruptor, which interrupts the exoskeleton development. It's a much more specific, targeted, and logical way to go."
Natural Alternatives
Some people, however, prefer natural alternatives. Dr. Warren Porter, a professor of zoology and environmental toxicology at the University of Wisconsin-Madison, is a proponent of natural methods of pest control. He maintains that EPA tests are flawed and cited studies showing that some pesticides can have long-term genetic and carcinogenic affects.
"You are putting a molecular bull in a china shop," Porter says. "The EPA doesn't ask if something is safe. It weighs the costs versus the benefits."
Porter recommends organic alternatives for fly control.
"Chickens are good fly predators," he says. "Baby powder-very fine powders-will suffocate fleas and bed bugs."
Diatomaceous earth is a natural substance that can be found in some feed-through products that are marketed to control flies. The FDA regulates it as a food additive for use as an "inert carrier" or "anti-caking" agent and requires that it not exceed 2% by weight of the total ration. Some anecdotal reports indicate that diatomaceous earth works to control flies.
"Diatomaceous earth contains diatoms, which puncture the exoskeleton, causing the insect to die," says Porter. "This is on the electron microscope level."
Diatomaceous earth is also used in swimming pool filtration systems, which has a much higher crystalline silica concentration than what is in food-grade diatomaceous earth. Therefore, you should make sure to use a product that is listed as food grade, conforming to FDA regulations.
Other feed-through products contain garlic, also thought to be a fly deterrent, though Farnam's Ross maintains that garlic doesn't work. A few years ago when market research showed garlic products to have the second-largest market share of feed-throughs, Farnam investigated it.
"Horses like garlic, so we developed a product that had as much garlic in it as a horse would eat," Ross said. "We gave it to 30-40 horses for a month, and then stopped feeding it to half of the horses and counted the flies. It did absolutely nothing."
Everyone's situation differs. Certainly, some geographic areas have more problems with flies than others. But if you practice good horse management, especially concerning manure control, and choose from among the many fly control products available, you can turn your facility into a no-fly zone.
