A change-over statistical design with complete balance of first residual effects was used with a tethered grazing technique to evaluate the effects of arthropod ectoparasites on the behaviour of adult Angus beef cows (Bos taurus; body weight (BW), 465+or-30 kg) grazing vegetative tall fescue (Festuca arundinacea cv Kentucky 31) in screened enclosures (5 m x 5 m x 2 m). Starved laboratory-reared stable flies (S. calcitrans) were released into each enclosure at 15-min intervals during 1-h grazing meals. Alighted flies were counted on body surfaces and rates of fly-induced movements recorded every 15 min. Treatments were: T1, 4 x 0 stable flies; T2, 4 x 125 stable flies; T3, 4 x 250 stable flies. Herbage dry matter (DM) mass (>5 cm) of the 25 cm tall sward was 3499+or-259 kg ha-1 and the herbage DM allowance (>5 cm) was 1.19+or-0.13 kg (100 kg BW)-1 h-1 when grazing started. Surfaces of cows assigned to T3 supported 42 alighted flies in the first quarter and their numbers increased linearly to 53 in the last quarter of grazing meals. Front legs supported 24 alighted flies in the first quarter and their numbers rose linearly to 35 flies in the last quarter. 9 flies alighted on hind-leg surfaces in the first quarter and their numbers increased linearly to 13 in the last. Alighted flies on the trunk declined from 7 in the first to 5 in the last quarter. Few flies alighted on cows' heads. Rates of movement of heads, ears, tails, and front and hind legs, and skin twitches increased (P<0.05) as more flies were released (T1-T3). Fly-induced movement rates of tail, hind-leg and skin twitches did not vary (P>0.05) throughout grazing meals. Front-leg movement rates increased linearly (P<0.05) as grazing meals progressed, whereas head and ear movement rates increased markedly (P<0.05) during the last quarter of grazing meals. Rates of biting in grazing cows declined linearly (P<0.05) as more flies were released and as grazing meals progressed. Stable flies also caused a linear decline (P<0.01) in the time spent at grazing stations, and the number of bites and DM mass of bites taken at each feeding station. Stable flies became more disruptive of grazing processes as grazing meals progressed; increasing numbers of alighted flies, especially on the front legs, caused head and front-leg movements that interfered with prehension and biting. Herbage DM intake rates were 0.49 kg (100 kg BW)-1 h-1 and were not significantly (P>0.05) affected by treatments, possibly because declining rates of biting were associated with increasing bite mass.
|Publication Title||Applied Animal Behaviour Science|
|Author Address||Department of Agronomy, University of Kentucky, Lexington, KY 40546-0091, USA.|
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