With high temperatures, heat stress can combine with attacks by stable flies to dramatically reduce weight gain in feedlot cattle, says Jack Campbell, University of Nebraska entomologist in North Platte.
Nebraska research indicates stable flies account for 71.5% of reduced weight gain of feeder cattle. Stable flies feed on blood, primarily on the front legs of cattle and the direct effect of the biting flies, including the energy loss involved in fighting them, accounted for 28.5% of the reduced weight gain of 0.31 pounds per day that was found in the studies.
Cattle bunch to protect their front legs, where the flies primarily feed, Campbell says, which can increase the effects of heat stress. Heat-stressed cattle reduce feed intake, increasing the time and the cost of feeding cattle in the form of increased yardage, feed, interest and labor.
While the need to control stable flies seems obvious, control requires considerable effort, according to Campbell. The flies breed in wet, decaying organic matter that is mixed with soil, a common environment in feedlot pens. The most common areas occur behind the feeding apron, adjacent to mounds, along and under fences where manure accumulates, the edges of potholes and along drainage areas. Spilled feed and organic matter used for bedding in sick pens also provide breeding areas, if wet.
Clearing out all of these areas is essential to fly control. Insecticide sprays can greatly reduce the adult population of flies. The chemical controls can be applied to areas where flies congregate by use of mist blowers, aircraft and hydraulic sprayers. The affected areas would include, cattle pens, windbreaks adjacent to the feedlots, shaded areas where flies rest during the day and vegetation near the feedlot pens.
Insecticides approved for this use are short-residual, low-toxicity products and will have to be applied frequently in the absence of sanitation and manure management.