Impact of Horse Flies (Diptera: Tabanidae) on Beef Cattle

Yearling Hereford heifers exposed to attacks by six species of horse flies (Tabanus abactor Philip, T. atratus F., T. equalis Hine, T. mularis Stone, T. subsimtlis Bellardi, and T. sulcifrons Macquart) with an average of 90 and 66 horse flies per animal per day for 84 days gained 0.08 and 0.10 kg per animal per day less than heifers protected from horse flies in 1982 and 1983, respectively. Average daily gain of heifers exposed to horse flies was 0.09 kg per animal per day less. These heifers were 16.9% less efficient in feed utilization than protected heifers. Greatest impact of horse flies occurred during the initial high attack rate at the end of the first 28-day period and throughout the second 28-day period when attack rate was highest. Potential total loss each year in weight gain in heifers exposed to tabanids for 84 days was >10.00 per head.