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Fly Control: Multi-Faceted Approach Yields Best Results

Ruth Wiechmann
for Tri-State Livestock News

It’s that time of year: that time when cattle stomp in the fence corners, swishing tails, swinging heads, fighting flies.

The flies are happy to swarm and return to get another taste and then settle in fresh manure to lay eggs. Cows are discontent with the pesky critters biting them and sucking their blood. Calves may not gain weight as hoped, cattle may contract fly-borne diseases such as pinkeye or foot rot thanks to the irritating insects.

Producers wanting to reduce the impact that face and horn flies have on their cattle herds need to consider tackling the problem on multiple fields, says Kristine Koepplin, DVM, a Livestock Nutrition and Animal Health Specialist working in New Salem and Elgin, North Dakota. External means including spraying, dusting, backrubbers or oilers can kill flies to reduce the population. Feeding garlic in salt or mineral can act as a fly repellent, making the cows smell less appealing to the hungry flies, and feeding an Insect Growth Regulator in mineral can interrupt the flies’ life cycle and reduce future population numbers. Overall herd health and balanced mineral intake is also crucial to fly control.

External means may be the most familiar to cattle producers. Back rubbers and oilers are a common sight in summer pastures as are medicated fly tags; when the flies get bad the spray pickup gets loaded up or a dust bag is filled and taken to the cattle to try to bring relief. Many products and many methods of application are available and producers can pick and choose the option that best fits their management practices and budget. Koepplin said that making sure to rotate between different drug classes is the key to reducing risk of future resistance problems in your fly population, for instance, alternating between permethrin based products and organophosphates.

Garlic as a salt or mineral additive may be a relatively new option, with less research to back it, but the saying that garlic breath will keep the riff-raff away probably holds true with cattle too. A Canadian study done in 2017 indicated over fifty percent fewer flies on a group of cows fed trace mineral salt with garlic powder at 2.1 percent of the weight of the salt when compared to two control herds fed trace mineral salt alone. Flies were counted monthly throughout the summer and the season long average on the cows in the herd fed garlic was seventy-five flies per head compared to 156 and 171 in the other two pastures. Fly avoidance behaviors were also observed and noted, such as tail swishing, head swinging, bunching, stomping and side licking. Again, the herd of cows fed garlic had consistently lower numbers of avoidance behaviors in comparison to the other two herds.

One study may not be enough for conclusive evidence, but it seems to indicate that feeding garlic can be beneficial. Anecdotal evidence from producers using garlic salt or mineral also seems to be positive.

“Think of the garlic as a mosquito repellent,” Koepplin said. “It doesn’t kill the flies but it seems to make the cows less attractive to them. While there are still a lot of unknowns regarding garlic use in livestock at this time, it seems to be an effective fly repellent and can be a key part of a producer’s management plan.”

Insect Growth Regulators (IGR) are natural biochemicals that interrupt the flies’ life cycle.

“When cattle eat a product containing IGR it passes through their system and lands in the manure,” Koepplin said. “Horn and face flies lay their eggs in the fresh patties but the presence of IGR prevents the larvae from developing. This ultimately reduces numbers of adult flies emerging and coming back to bite the cows again. IGR mimics naturally occurring insect biochemicals responsible for insect development instead of through direct toxicity. This makes it effective at very small concentrations. It has been researched extensively over twenty to thirty years and has shown no negative effects on beneficial insects such as dung beetles and has no known horn fly resistance.”

Ideally, producers should start feeding IGR thirty days before flies emerge in the spring, but Koepplin says it’s never too late to start.

“Even though you might not see a huge difference this year if you start feeding IGR now, you will reap the benefits next year,” she said. “By feeding it now you are breaking the life cycle and preventing the larvae from hibernating over winter to emerge in the spring.”

IGR should be started thirty days prior to the last frost in the spring and continued for thirty days past the first frost in the fall for best results. This helps prevent horn fly larvae from overwintering and gives producers a jump start on the next fly season.

Nutrition is the other key factor involved in fly control in cattle. Producers need to be aware that environmental factors can throw a herd’s mineral balance off particularly as summer progresses and water sources become stagnant or grain crops are used as forage. Even with the best mineral supplementation, nitrates in feed and sulfates or iron in water sources can tie up key trace minerals making cattle more susceptible to fly borne diseases.

“Think of all the trace minerals as a ball or a globe,” Koepplin said. “They all interact with each other in perfect harmony, but if one or two get tied up it throws it all out of balance.

“For example, zinc and copper are two minerals that can be tied up by the presence of high sulfates; even if cattle are eating sufficient amounts in their mineral if it’s tied up it passes right through them and is not absorbed. Zinc is crucial to the development of the cornea of the eye. If this protective layer is weak due to zinc deficiency, animals are more susceptible to pinkeye. Copper deficiency can be linked to a weakened immune system and reproductive problems. If copper gets tied up you might see more open cows in the fall. Molybdenum is an elemental trace mineral sometimes found in forage that can also tie up copper. If feed sources test high in molybdenum additional copper may need to be added to the mineral ration.”

While fly control programs will never eliminate all of the flies, they can go a long way toward keeping cattle healthy and comfortable through the summer. Best results can be obtained by making sure minerals in the diet are balanced and using multiple modes of action to combat the pests: IGR to interrupt the flies’ life cycle, garlic as a repellant, and external products to kill adult flies.


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