Facing a Growing Fly Problem
It appears we may have underestimated the impact stable flies have on the beef industry. They are known bloodsuckers capable of spreading infections and inflicting considerable aggravation upon cattle. But stable flies have often been considered a pest more common to operations where cattle are kept in confinement — feedlots and dairies. Horn flies and face flies are typically targeted as the summertime pests of most concern for cattle on range and pasture.
Twenty years ago, the cost of stable flies to U.S. cattle production was thought to be about $608 million per year. However, a report co-authored by USDA Agricultural Research Service (ARS) Entomologist David Taylor says stable flies may cost the country's cattle industries more than $2.2 billion annually, making them the most damaging insect pest affecting cattle. Research by Taylor and his colleagues suggests the annual economic impact to dairy and feedlot operations is $360 million and $226 million, respectively. The estimated impact to the cow-calf segment is $358 million. For stocker cattle on pasture, it's $1.3 billion.
The estimated losses were based on reductions to milk production in dairy cows and reductions in weight gains among calves (preweaning), stockers and feeder cattle. Not accounted for are stable fly effects on feed conversion or animal breeding success. Neither do the estimates include costs of damage to pasture and water quality that result from the behavior of animals trying to elude stable flies.
Entomologists say stable flies feed mostly on the legs and feet of host animals, particularly the front limbs, and their bite is painful. When cattle bunch in a corner of the pasture, stomping their feet and swishing their tails, it's usually because of stable flies. Repeated bunching can degrade areas where cattle congregate to fight flies. Given the opportunity, infested animals often wade belly-deep into ponds or creeks, which degrades water quality and may increase the incidence of infections such as foot rot. Whatever the fly-fighting behavior, cattle spend less time grazing and undergo increased levels of stress. Bunching together during hot weather also increases heat stress.
Fly control measures, such as backrubbers, dustbags and insecticide-impregnated ear tags, are less effective for stable flies than for other fly species that accumulate on animals' backs, upper bodies and faces. Applying insecticide sprays to the legs of cattle can have some beneficial effect, but it seldom lasts long. The effect is particularly short-lived if residual insecticide rubs off as cattle travel through tall forage.
The experts suspect certain management practices may have contributed to stable flies becoming a more significant problem across all segments of the cattle industry. Widespread use of bale feeders is considered a likely factor. Stable flies lay their eggs in piles of moist organic material, including hay and straw. When bale feeders are used in concentrated feeding areas, the resulting buildup of wasted hay, manure and urine makes a nearly ideal breeding environment for stable flies. It's estimated that up to a million stable flies may develop in the residue from a bale feeding site. Unlike some other species, adult stable flies can travel for many miles.
Management steps that can help control stable fly populations include using bale feeders designed to limit the amount of hay that falls out of the feeder and is trampled. Moving feeders frequently can help prevent excessive accumulation of trampled hay and animal waste at certain sites. After moving feeders, spreading accumulated residue will allow it to dry. Rolling out big bales when feeding cattle will limit accumulation if bales are not unrolled in the same area repeatedly.
