On summer days, it’s not just the heat that challenges Rachel Gray’s cattle – it’s also cattle flies.

Horn flies in particular can become stressful for all cattle. In the U.S. beef industry alone, horn flies cause an estimated loss of $1 billion annually due to the negative impact an infestation can have on livestock weight gain.

At Little Timber Farms, one of the most persistent pests we battle is the horn fly. These small, dark flies cling to the sides, backs, and necks of cattle, feeding on blood and causing irritation.

A few flies are a normal part of livestock management and don’t concern me. But when the fly load is heavy, cattle will bunch up in the pasture, swishing their tails nonstop, and even stop grazing. That’s when it becomes a problem.

Why Numbers Matter with Cattle Flies

My cows aren’t just uncomfortable when covered in cattle flies; they’re at risk of health issues. Cattle have a herding instinct that causes them to bunch together. When animals bunch together in warm weather and try to swish flies off of each other instead of spreading out to graze, they tend to overheat. The cows in the middle of the bunch are also likely not eating or drinking. When cattle stop eating, their stomachs — specifically the rumen — stop working properly. Ruminants (a term we use for cattle, sheep and deer) have rumens, a large stomach compartment where microbial fermentation helps break down all that tough plant matter so it gets absorbed instead of passed through. 

A cow’s rumen is amazing, but it needs a steady supply of forage to function at its peak. Fly pressure disrupts this rhythm. Without grass or feed constantly moving through the stomach, gastrointestinal issues can occur, the cattle start to feel ill, and ultimately lose weight. It’s similar to when humans do not eat and drink throughout the day. We start to feel bad, we get dehydrated and we start to feel bad.

That’s why keeping an eye on fly load — the amount of flies on an animal — is critical.

How we Control Cattle Flies

We’ve tried different approaches to control cattle flies over the years — kind of like the different options pet owners use for fleas, ticks, worms and mosquitoes. For example, fly tags work a bit like flea collars, feed-through products are similar to giving your dog a chewable preventative, and pour-ons are like the topical drops you might put on a cat or dog’s back. Just like with pets, keeping flies under control takes some trial and error and guidance from your veterinarian. For our herd, we’ve found a simple topical spray from our vet gives us the best results.

When checking our cows for pregnancy via ultrasound, they receive 12 mL of a topical insecticide spray that provides protection from cattle flies for about six weeks. It takes very little product to be effective.

We avoid feed-through products because they can harm beneficial insects in the pasture once the cattle pass them through. Stewardship of both the land and the herd (aka raising regenerative beef) are our goal here, so a topical application is currently our best option.

Stewardship in Action

Fly management isn’t about eradicating every insect. It’s about keeping fly pressure low enough that our herd can graze, drink, and thrive without too much disruption. By choosing targeted tools and using them sparingly, we protect animal health while respecting the ecosystem they depend on.

At the end of the day, healthy cattle make for healthy beef. And something as small as a horn fly can make all the difference in raising content, healthy livestock.