MODERATION OF GRAZING BEHAVIOR OF BEEF-CATTLE BY STABLE FLIES (STOMOXYS-CALCITRANS L)

Grazing beef cows (Bos taurus L.) were exposed to stable fly (Stomoxys calcitrans L.) and their reactions were related to ingestive behavior . Three concatenated latin squares (4X4) were used to evaluate the eff ects of stable flies on the behavior of Angus cows grazing vegetative tall fescue (Festuca arundinacea Schreb. cv Johnstone) in screened enc losures. Four populations (0, 50, 100 and 150) of starved, laboratory- reared stable flies were released into each enclosure at 15 min interv als during 1 h grazing meals. Mean numbers of alighted stable flies in creased linearly with treatment level up to 125 per animal and up to 4 6 on forelegs and up to 7 on hindlegs. Dorsal and ventral trunk surfac es each supported up to 35 alighted flies. Alighted fly numbers increa sed on all major body sectors as grazing meals progressed: when 150 st able flies were released, there were 25, 44, 56 and 63 flies on forele gs during successive quarters. Releases of up to 150 stable flies caus ed linear increases in fly-induced movements of heads (to 1.9 min-1), ears (to 4.5 min-1), skin twitches (to 18 min-1 per side), tail swishe s (to 36 min-1), forelegs (to 1.4 min-1) and hindlegs (to 0.8 min-1). Stable flies caused linear increases in herbage dry matter (DM) intake (0.50-0.58 kg (100 kg body-weight (BW))-1 h-1), and bite DM mass (fro m 1.0-1.4 g) and a linear decline in rate of biting (from 41-35 biles min-1). Cows visited 3.2, 3.9, 4.3 and 3.4 feeding stations min-1 inge sting 16.1, 12.6, 10.9 and 16.0 g DM per feeding station when four pul ses of 0, 50, 100 and 150 stable flies were released, respectively. Bl ood intake of engorged stable flies declined from 9.3 to 8.1 mg, eithe r indicating competition between flies for feeding stations or deterre nt actions of their hosts disturbed their feeding. Moderation of inges tive behavior of cows was attributed to annoyance of low populations o f alighted flies. In the presence of stable flies, cattle may accelera te herbage intake and reduce grazing times.