Losing a Dollar a Day? The True Cost of Horn Flies on Cattle Performance

Little things have a big impact — and in the case of horn flies, it’s a big economic one. 

“When you think about fly control and specifically the horn fly, it is by far the number one nuisance that beef cattle on pasture experience,” says Johnathan Wells, beef field representative for Cargill Animal Nutrition. 

Horn flies transfer diseases such as anaplasmosis and mastitis, but treatment costs aren’t the only way they impact the bottom line. These tiny pests also chip away at average daily gain. 

“You’re looking at average daily gain differences of about 15% — that’s roughly a third of a pound per day,” says Wells. “In this market, that’s over a dollar per day in lost performance.” 

Cattle with heavy fly loads use more energy than those with minimal pressure. 

“You have an animal that goes from about 76 beats per minute to over 100 beats per minute under a heavy fly load — that’s a 30% increase in heart rate,” Wells explains. 

That increase in heart rate leads to higher water intake and greater urine output. As urine output rises, nitrogen retention decreases — and that’s where the loss in average daily gain shows up. 

“You’re looking at average daily gain differences of about 15% — that’s roughly a third of a pound per day,” Wells says. “In this market, that’s over a dollar per day in lost performance.” 

Controlling flies isn’t new, but evolving methods are worth considering — especially as resistance to traditional products becomes more common. 

“Most common products are targeting the adult fly after it’s already affecting the animal,” says Wells. “That’s where we’re running into resistance.” 

Targeting the egg stage instead of the adult fly offers a different approach. Feed-through products, such as Altosid, work by interrupting the fly’s life cycle. 

“Altosid works by breaking the life cycle of the fly — it prevents eggs from developing into adult flies,” Wells explains. 

However, feed-through solutions require consistent intake to be effective. 

“A lapse of even a couple weeks in a feed-through program can undo months of progress,” Wells says. 

That inconsistency can come from variable mineral consumption or supply issues at the feed store — both real-world challenges for producers. 

An alternative is the Altosid IGR XRB bolus, which delivers the same active ingredient without relying on daily intake. 

“With the extended-release bolus, you apply it one time and get about 195 days of control,” Wells explains. 

The bolus helps ensure consistent delivery while reducing the need for repeated applications. 

“Once you put it in, you know it’s in the animal — that consistency matters,” he says. 

No matter the method, it’s important to keep expectations realistic. 

“The goal is reduction — you’re still going to see some flies, but you’re controlling the population,” Wells says. 

And controlling that population directly impacts profitability. 

Listen to the full conversation on the Casual Cattle Conversations podcast.