Measures of The Direct Impact of Hematophagous Flies On Feeder Cattle: An Unexpectedly High Potential Economic Impact

Abstract Beside blood pathogens transmission, insects of the order Diptera affect livestock by visual and contact harassment; blood-feeders are responsible of painful bites and blood despoliation, generating behavioural modifications, anaemia and production losses. Knowledge of their economic impact is a basis for cost-effective control. Here, we measured the global impact of Diptera by comparing two batches of six feeder cattle, one in open air, the other protected by a mosquito net. Analytical data were: insect density in open air, and, for feeder cattle: tail-flick counts, hematocrit values (Ht), feed intake, feed conversion ratio (FCR) and live body weight gains (LBWG). Over a period of five months, results showed significant losses of LBWG of cattle exposed to insects, estimated at 8.0±1.5 Kg/month [2.7;13.3], with a total loss reaching 40.0±5.5 Kg/head. Main diurnal insects were Stomoxys spp. and M. crassirostris. There was a strong correlation between fly density and diurnal tail-flicks. Night trapping and tail-flicks showed a potentially important role of mosquitoes to be further explored. Ht of exposed animals was 3-4% lower than controls. FCRs indicated that exposed animals needed 33% more dry matter intake/Kg of LBWG. Economic assessment showed that dipterans were responsible of 10-11% loss of LBWG during the main growing period of feeder-cattle (10-15 months). A feedlot of 100 calves would register a total loss of 16,000$ within 5 months, which appears to be an unexpectedly huge loss caused by dipterans. Investing part of this money in fly control would probably be beneficial.