Face-fly pest intensity, fly-avoidance behavior (bunching) and grazing time in Holstein heifers

Abstract

The relationship between face-fly (Diptera: Muscidae) feeding, fly-avoidance behavior (bunching), and grazing time (monitored by vibracorder units) was examined in herds of Holstein heifers either exposed to ambient pest intensity or treated to suppress fly-feeding. The data show that the number and duration of bunching episodes was significantly greater in herds exposed to ambient face-fly activity; also, positive correlations were observed between pest intensity and the number and duration of bunching episodes. Heifers with faces protected by bunching were exposed to significantly fewer flies than heifers prior to bunching or on the periphery of the aggregation. Total grazing time did not differ between herds, and there was little difference in diel grazing patterns, which suggests that bunching represents modified non-grazing behavior rather than displaced grazing time. © 1982.