Controlling horn flies makes economic sense. Managing the load of internal parasites in cattle can boost returns. Combined, these two practices yield even more.

That’s the bottom line of a study conducted at Louisiana State University (LSU). Researchers there released the results last month.

The study looked at growing cattle on bermudagrass pasture. There were three annual trials from May to August – 56 calves in each trial – split into four treatment groups: untreated control (CON), cattle treated for horn flies with insecticidal ear tags (HF); calves treated for gastrointestinal nematodes (GN) with an anthelmintic; and cattle treated for both (HF-GN).

You can see the specific results in the table below, and you can find the entire study here.

The bottom line was that treating cattle for both horn flies and internal parasites resulted in significant weight gains of about 29 lbs. average – the length of each trial ranged from 84 to 112 days. Compare those 29 lbs. to the $6.75/head treatment cost, excluding labor.

By way of comparison, when compared to the control group, neither the HF calves nor the GN calves yielded statistically significant weight advantage compared to the control group.

LSU researchers suspect three possible causes for the lack of effect in controlling horn flies alone: the level of fly control achieved in the treated group was marginal; the overall horn fly population was beneath the economic threshold in one trial and barely above it in another; and the magnitude of weight gain of all stockers in the study was relatively low.

Similarly, researchers attribute the overall low gain levels to the lack of significant weight gain observed in the GN calves compared to the control group.

Tables for LSU Stocker Trials

Trial 1

Treatment
In-wt.
(lbs.)
ADG
(lbs.)
Out-wt.
(lbs.)
Control 564 0.82 632
Horn Fly (HF) 558 0.80 623
GI Nematode (GN) 558 1.01 642
HF-GN 559 1.11 650

Trial 2
Treatment In-wt.
(lbs.)
ADG
(lbs.)
Out-wt.
(lbs.)
Control 564 0.76 639
Horn Fly (HF) 560 1.05 663
GI Nematode (GN) 562 1.28 688
HF-GN 559 1.11 650

Trial 3
Treatment In-wt.
(lbs.)
ADG
(lbs.)
Out-wt.
(lbs.)
Control 559 0.99 669
Horn Fly (HF) 559 0.98 669
GI Nematode (GN) 560 1.03 675
HF-GN 559 1.10 682

Tables from: Evaluation of Horn Flies and Internal Parasites with Growing Beef Cattle Grazing Bermudagrass Pastures by S.M. DeRouen, et. al, Louisiana State University.