May 23 2024 11:08 AM

    In our barns, flies are the top cause of bunching cows.

    It’s the time of year in Kansas when the fly season begins. Our cows are housed in an open-sided freestall barn, and we started to notice a few weeks ago that the fly pressure was starting to creep up.

    It seems that even in the best of scenarios, we deal with some flies each year, making us an expert in both the consequences of flies and the best ways we can combat them.

    The biggest stressor caused by these stable flies is afternoon bunching. In a study referenced in a recent Buckeye Dairy News article, just one fly per cow leg can cause cows to bunch in freestall barns.

    “The stress of the fly bites causes cows to stand in a tight group with their heads to the center of the group and their tails to the outside to protect themselves against the stable fly attack,” Dwight Roseler explained in the article. “Fly repellent behaviors include tail flicking, foot stomping, head tossing, skin twitching, and ear trembling to reduce the fly attack.”

    We certainly notice some of these fly avoidance behaviors in our barn when and if the fly pressure gets too high. Our greatest concern with bunching is the impact it has on welfare and health. As Roseler, the Ohio State adjunct professor described, bunching intensifies cows’ risk of lameness and restricts feed intake and milk production.

    “When cows bunch together, it compromises production, health, and welfare of the animals. Bunching increases heat stress of the affected cows, increases standing, splashes manure on the udder, and elevates stress hormones,” Roseler continued.

    For that reason, fly control measures must begin well before the flies appear on legs.

    “An effective fly control program must include a combination of cleanliness, larval control through feed, regular sprays, ear tags, and parasitic wasps. Fly control must start early (April/May) to prevent mid to late summer fly issues,” Roseler detailed.

    We have tried most of these fly preventatives, and we’ve had the most luck with a feed additive and regular insecticide spraying. We have also utilized application of fly bates around and inside our barns when the weather permits. I have also noticed that cows do better when we have our fans operational and the Kansas wind is blowing strong.

    I wish you the best of luck as you battle bunching cows and those awful flies.

    Maggie Gilles

    The author is a dairy farmer in Kansas and a former associate editor at Hoard’s Dairyman. Raised on a 150-cow dairy near Valley Center, Kansas, Maggie graduated from Kansas State University with degrees in agricultural communications and animal sciences.