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Does Double Protection = Increased Gain

By: Loretta Sorensen

Kansas State University researchers organized a study using stocker calves to help determine if two insecticide-impregnated ear tags control horn flies more effectively than one. They conducted their research in native pastures in the Flint Hills region of Kansas. Dale Blasi, KSU Extension Beef Specialist and research team member, says extremely dry conditions occurring in 2012 hampered his team’s effort to obtain definitive findings.

“Because it was so dry we took calves off pasture earlier than we normally would,” Blasi says. “Our findings would have been more conclusive if we had been able to replicate our research in additional pastures. In 2012 that just wasn’t possible. Even with an expanded study, there are so many variables from pasture to pasture it’s difficult to say that fly control provided by two ear tags versus one tag significantly improves overall gain and growth in stocker calves.”

KSU’s 77-day grazing study began in April 2012 at the Kansas State University Beef Stocker Unit. All 267 steers in the study were in sound health when the study began. Off-test weights, collected at the conclusion of a previous study, were used to randomly assign each animal to grazing treatments. Steers were assigned to three treatments with four pasture replicates per treatment. Treatment groups included a no-ear-tag control, one insecticide ear tag per calf or two insecticide ear tags per calf.

Grazing paddocks were stocked at 253 pounds of beef/acre. Calves were injected with 2mL of Bovi-Shield Gold 5 and poured with UltraBoss insecticide. Corathon (15% Coumaphos, 35% Diazinon) insecticide ear tags were administered at the time cattle were placed on pasture April 24, 2012. Paddocks were randomly assigned to treatment and served as the experimental unit. Individual weights were recorded at completion of the study. Under normal grazing conditions, cattle are removed the end of July. Due to drought conditions, all calves in this study were removed from pastures July 10, 2012.

At the conclusion of the study, calves with no ear tags showed 110 pounds of gain. The one-tag control group showed 119 pounds of gain and the two-tag group showed 122 pounds of gain.

While the study results were somewhat inconclusive, controlling flies results in increased animal performance presumably from a lower rate of animal irritation.

“It’s important to rotate the type of chemical in ear tags every year to avoid insecticide resistance,” Blasi says.

Recording yearly insecticide brands facilitates rotation strategies. In addition to changing brands, producers should select insecticide-impregnated ear tags that provide a different mode of action. Some tags contain two modes of action in one product.

Monitoring animals to verify that fly numbers on each side of the animal reaches approximately 100 (it takes more than 100 flies per side to impact weight gain) prior to tagging helps ensure insecticide effectiveness throughout fly season. 

Fly control strategy should include supplements provided by a combination of dust bags, oilers, sprays or pour-ons as warranted.

Among the ways ear tag effectiveness can be reduced include tagging cattle too early, abnormally high numbers of flies and wet conditions that promote increased development of fly larvae in moist manure.

Insecticide in ear tags is transferred to the animal’s hair coat when cattle groom or rub. Typically, the insecticide is effective for 12 to 16 weeks after animals are tagged. If tags are inserted too early, insecticide effectiveness ends before fly season does. If horn flies from nearby untreated cattle move into an ear-tagged herd, insecticide effectiveness may appear to be less successful.

Because ear tag costs average $2 per tag, cost doesn’t usually prohibit the added insurance of a second tag. Still, scientific evidence of advantages found in using two tags has remained elusive.

“I believe it’s a good idea,” Blasi says. “Even with last year’s short grazing season, our testing didn’t demonstrate significant gain differences between the one-tag and two-tag control groups, but the grazing season wasn’t typical, either. We want to report our findings and allow producers to draw conclusions about the best options for their operation.”

A full report on the KSU study is available at www.ksre.ksu. edu/bookstore/pubs/srp1083.pdf.      

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