Pros and cons of feeding an insect growth regulator

Horn flies create a pesky and expensive problem for producers. Some estimates indicate losses due to horn flies on cattle populations in the United States top $800 million each year. 

The irritating insects inflict the greatest toll on momma cows and growing calves. The constant biting causes annoyance and blood loss in animals. This leads to energy loss due to fighting off the flies, decreased grazing and lower milk production. Horn flies can also be the source of the spread of summer mastitis in non-lactating mammary glands. 

Feed-through fly control

One effective tool to control the horn fly population in herds is the use of feed-through fly control. Feed-through fly control can be found in tub, block, feed additive or loose mineral form. 

Feed-through fly control contains a product called insect growth regulator (IGR). When an animal consumes the insect growth regulator it passes through the animal’s feces and prevents the fly larvae from developing and reaching maturity. “Depending on the active ingredient used, it may just control horn flies (Methoprene) or it may control horn, face, stable and house flies (Tetrachlorvinphos or Diflubenzuron),” Elizabeth MacConnell Picking, University of Missouri Extension Livestock Specialist, said. 

When to use feed-through fly control

Producers should start feeding a feed-through product 30 days before the last frost in the spring and 30 days past the first frost in the fall. “When fed before flies start to emerge, a feed through fly control product can minimize flies from hatching from manure piles, reducing fly bites that make livestock uncomfortable, reduce weaning weights and cause infections like pinkeye and mastitis,” Picking explained. 

The Pros

The IGR products prevent fly maggots from maturing, therefore reducing the fly population that causes a variety of problems for livestock. In addition, feed-through fly control works well in combination with other fly control methods. “In some situations, it is beneficial in terms of using another method of control to rotate into the program, so you won’t develop insect resistance,” Dr. Kelly Loftin, University of Arkansas professor and entomologist, said. 

Another benefit of feed-through fly control comes with its ease of use. Producers don’t have to run cattle through a chute like they would to apply pour-ons or sprays. 

The Cons

IGR fly control requires patience. If producers wait to start feeding the feed-through fly control after adult flies are present, the results will be delayed. “The key to using insect growth regulators is the producer needs to keep in mind that it has no effect on adult flies,” Loftin stated. “Producers need to have a little bit of patience and understand it is not going to be immediate.”

Additionally, producers need to make sure their animals are consuming the recommended portion of the feed-through fly control each day. “If the animal is only getting a partial dose, it is not going to be that effective,” Loftin added. 

Another challenge includes the product’s effectiveness decreases if cattle are in close proximity to an untreated herd. “The downside of relying solely on a feed-through product for fly control occurs when neighboring farms do not use a feed-through fly control product and flies are able to migrate,” Picking stated. 

Picking suggests using a combination of feed-through fly control products with other control methods like sprays, pour-ons, impregnated tags, or dust baths.


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