Individual and group behaviour of pastured cattle in response to attack by biting flies

In 1983 and 1984 the impact of biting flies on the behaviour of pastured heifers was determined for 2 herds of cattle in eastern Manitoba, Canada. One herd received a whole-body spray of cypermethrin (0.1% a.i.) per animal every 14 days and the other was an untreated control herd. Horse flies (11 species, predominantly Hybomitra spp. (10 species) and particularly H. pechumani) were the most bothersome to the heifers, with peak numbers of flies mostly occurring between 11:00 and 15:00 h. Horse flies and mosquitoes (14 species, all except one being Aedes spp., especially A. punctor and A. vexans) caused an increase in individual avoidance responses of the animals, including head tosses, foot stomps, ear flicks and tail switches. In 1983, the numbers of tail switches and foot stomps were significantly higher in the control herd, and in 1984, the numbers of head tosses were significantly higher in the treated herd. The formation of grazing lines and bunching were the most prevalent herd responses to biting fly attack. Stampeding was observed only under the most extreme mosquito pressure. Using canonical discriminant analysis on behaviour data, significant differences were identified in behaviour before and after 10 July 1984. Similarly, animals treated with cypermethrin displayed significantly fewer behavioural responses to biting fly attack than nontreated animals.