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Does your cow worry about flies? Yes

May 17, 2021

Here is a refresher on identifying and treating horn and face flies in beef herds.

By: Mindy Ward

If your cattle are stomping, grouping up, twitching tails or licking their backs trying to rid themselves of flies, it is a sign of anxiety. The behavior is actually a syndrome pegged by veterinarians as “fly worry.”

“It’s this activity that cows and calves will do in order to try to address the fly population themselves if there’s no insecticides being used in the system,” University of Missouri Extension veterinarian Craig Payne says.

The condition, left unchecked, can cause cattle to reduce feed consumption and lose weight. Payne says studies of stocker cattle show calves with fly control gain anywhere from 15 to 30 pounds during the grazing season compared to those without control measures. So, whether a farmer treats for flies has an effect on the beef operation’s profitability.

Types of flies in cattle

Beef producers should be on the lookout for horn flies and face flies that make cattle uncomfortable this time of year. But Payne says it is the horn fly the causes the most economic damage.

Adult horn flies have brownish-gray or black bodies and are shiny. “With horn flies, you can identify them simply by where they’re located at on the animal,” Payne explains during an MU Forage and Livestock Town Hall. “So, they’re going to be found in the shoulders, neck region, maybe on the underbelly.” Horn flies tend to spend the majority of their life on the animal.

By far, horn flies are going to represent the most significant economic impact to the beef herd, Payne says, and that’s because of the aggressive feeding behavior. Horn flies require a blood meal for egg production, which means they feed upward of 40 times a day on cattle. This excessive feeding on the animals creates stress.

Unlike horn flies, face flies are nonbiting flies that cluster around an animal’s eyes and mouth. They also gather around open wounds. “Where our concern is at with face flies is their potential to contribute to pink eye issues,” Payne says.

However, these flies despite their name do not stay long on the face. Instead, they spend most of their time on other objects or along waterways, making control more difficult. Face flies peak in July and August.

Farmers seeing either of these, along with symptoms of fly worry, should treat their cattle.

Tag beef cattle

Fly tags are the most common control method among cattle producers.

Payne says the tags are embedded with either an organophosphate compound or a pyrethroid. The insecticide is released from the tag, but it doesn’t only stay up in the head and neck region, Payne explains. It actually disperses across the hair coat of the animal.

Companies advertise fly tags to be effective up to five months. However, Payne says realistically it is about 12 to 15 weeks. So, farmers need to time when they will place the tags in cattle.

“If they apply too early, by the end of summer when fly control populations start to reemerge, the compound will be out, and you are not going to get the length of control you expect,” Payne warns. He recommends farmers apply fly tags when they see about 200 flies per animal — but since counting flies is difficult, he adds, “That would represent about the number of flies that fit in the palm of your hand.”

The number of tags depends on body size. Typically for a mature cow, fly control can be realized with two tags. For younger calves, it would be one tag.

“If the calves are paired with the cows, as the cows groom those calves, some of that insecticide from the ear tag off the cow is going to get on the calf and help provide some control as well,” Payne adds. He recommends using only one class of insecticide and not mixing and matching on an individual animal.

Talking to companies that sell fly tags, Payne finds, they receive a lot of complaints after rain events. What happens is the rain washes off the insecticide, and at the same time, there is an increase in fly population because of moisture.

“What will eventually happen is that insecticide will redisperse within five days to a week, and you’ll go back to a control level as long as your tag is still effective,” he adds. “So, if you do experience that and you’ve placed flight tags, don’t run to the phone and call your animal health representative, just give it a little bit and those will go back to a level of fly control you expect.”

Additional fly control options

Fly tags are not the only way to control populations. Payne offers a few more fly control methods for cattle producers.

Sprays or pour-ons. These products will immediately kill flies, but this is a one-time treatment as sprays do not provide much residual control. Payne warns cattle producers will have to use these more frequently, anywhere from seven to 21 days depending on fly activity and weather. This adds labor for the farmer and sometimes stress to the animal.

Farmers should also avoid generic dewormers as a method of fly control. He warns frequently using these products can lead to building up resistance for parasite control.

Feed through control. This prevention method includes insect growth regulators, or IGR, that can be fed through mineral or tubs. It’s designed to break the life cycle of the fly. Start feeding IGR at least two weeks before fly season. While the method brings with it little labor for the farmer and low stress on the animals, it is costly.

Dust bags. Back rubber dust bags can be used, but cattle need to be forced to use it frequently, Payne says. These should be used in areas where cattle are required to go under them in a gateway, around a mineral feeder, or any other high-use area. This method also requires farmers to recharge the bag every two to three weeks for optimum fly control.

Regardless of fly control method, Payne says using multiple methods together is a good idea. “Using a feed-through and also tags are going to give you the best control,” he says.

Fly resistance is real

Beef producers should rotate active ingredients or types of insecticide to thwart resistance. Payne recommends using two years of organophosphates, then one year of pyrethroids.

“One thing you will notice with organophosphates is they don’t necessarily do a good job at controlling face flies,” he adds. “To my understanding, they are going to be a little bit higher when you go to that organophosphate rotation. So, you may just have to grin and bear it during that time.”

Payne says farmers should remember the primary focus during fly season is control of the horn flies because of their economic impact to the farm.

One more reminder: Don’t leave fly tags in after the fall. Resistance comes after a continual exposure to a drug, even at low levels, Payne says. “If we applied those tags, we need to be cutting them out in the fall to avoid low-dose exposure,” he says.