P. L. Cornelius

Stable flies (Stomoxys calcitrans L. ) and the behavior of grazing beef cattle

Abstract A change-over design with complete balance for first residual effects was used with a tethered grazing technique to evaluate the effects of arthropod ectoparasites on the behavior of adult Angus beef cows ( Bos taurus ) (body weight (BW), 465 ± 30 kg) grazing vegetative tall fescue ( Festuca arundinacea Schreb. cultivar ‘Kentucky 31’). The three treatments were: T 1 , open grazing plots with exposure to natural ectoparasite populations; T 2 , grazing plots with exclosures (5 m × 5 m × 2 m) to minimize natural ectoparasite populations; T 3 , similar enclosures containing 2500 laboratory-reared adult stable flies ( Stomoxys calcitrans L.). At the start of grazing, herbage dry matter (DM) mass (> 5 cm) of the 25 cm sward was 2882 kg ha −1 and the herbage DM allowance (> 5 cm) was 1.0 kg (100 kg BW) −1 h −1 . Nine flies alighted on cows in open plots (T 1 ), very few ( 2 ) and 108 stable flies alighted on cows in the enclosures (T 3 ). Of the latter, there were 67 on front legs, 30 on hind legs and seven on the trunk. Stable fly populations on the body surfaces of cows declined logarithmically during grazing meals. During the first part of grazing meals, stable flies induced cows (in T 3 ) to move their heads (8 times per minute), and to lift their front legs (8 times per minute) and hind legs (3 times per minute). Stable flies also induced ear movements (12 per minute), tail movements (69 per minute) and skin twitches (25 per minute). Rates of stable fly-induced behavior declined logarithmically during grazing meals. Cows in T 1 , T 2 and T 3 visited 4.2, 3.9 and 3.1 feeding stations per minute, respectively, but rates of herbage DM intake were not affected by the presence of stable flies ( P > 0.05) and averaged 0.35 kg (100 kg BW) −1 h −1 . In the absence of stable flies (T 2 ), rates of biting of cows declined logarithmically from 46 to 30 bites min −1 . Cows subjected to stable flies (T 3 ), however, started grazing at 19 bites min −1 and ended grazing meals at 26 bites min −1 . Mean herbage DM intakes per bite were 833, 694 and 1011 mg for T 1 , T 2 and T 3 , respectively.

Behavior of grazing cattle exposed to small populations of stable flies (Stomoxys calcitrans L.)

Abstract Cattle grazing in the presence of low-level infestations of stable flies (Stomoxys calcitrans L.) may offset reductions of grazing time by increasing their rate of herbage intake, and this may contribute to the determination of economic threshold populations. On four consecutive days, we released four pulses of 50 or 100 laboratory-reared stable flies at 15 min intervals over 1 h in screened enclosures, according to a balanced change-over design. Within these enclosures, fasted, adult Angus cows (Bos taurus L.) (body weight (BW) 465 ± 30 kg) grazed vegetative tall fescue (Festuca arundinacea Schreb. cv. ‘Johnstone’) at herbage dry matter (DM) allowances of 1.4 kg (100 kg BW)−1 h−1. Alighted fly numbers on body surfaces of cows were similar during each quarter of grazing meals, and numbers of alighted flies increased linearly as more were released. Cows exposed to colonies of 100 stable flies had 16 alighted on fore legs, 5 on hind legs and 5 on trunks. Stable flies weighed 6.1 mg before and 17.7 mg after feeding. Fly-induced behavior of grazing cows did not vary significantly (p > 0.05) within grazing meals, and releases of up to 100 stable flies caused linear increases in movements of heads (to 3.3 min−1), ears (to 3.7 min−1), skin twitches (to 14 min−1 side−1) and tail swishes (to 36 min−1), but had little effect on movements of fore and hind legs (

Ingestive behavior of beef heifers within grazing sessions

Abstract Two field experiments were used to measure the net effects of changing hunger and satiety on the ingestive behavior of tethered beef cattle ( Bos taurus ) within grazing sessions that followed overnight fasts. Angus heifers [liveweight (LW), 364±8 kg] were grazed on a vegetative tall fescue ( Festuca arundinacea Schreb.) pasture with a herbage mass of 4.5 t ha −1 of dry matter (DM) and herbage DM allowances of 5.5 kg per heifer h −1 . During their first hour of grazing, heifers ingested herbage DM at 0.65% LW h −1 and took bites of 1 g DM at 41 bites min −1 . After 45 or 90 min of grazing, heifers were consuming herbage at 0.51% LW h −1 and forming bites of 0.9 g at 37 bites min −1 . In the second experiment with twice the herbage DM allowance (11 kg per heifer h −1 ) and slightly higher herbage DM mass (5.6 t ha −1 ), heifers ate herbage at 0.76% LW h −1 and took bites averaging 1.2 g (DM) at 36 bites min −1 during the first hour of grazing. Heifers in their second or third hour of grazing ate herbage at 0.48% LW h −1 and took bites of 1 g at 29 bites min −1 . The decline in rate of intake within grazing sesssions was attributed to declining hunger and increasing satiety. Rates of herbage intake of animals grazing temperate swards unrestricted by allowance and availability of herbage are ∼ 0.5% LW h −1 after hunger is alleviated.

Herbage allowance and intake of cattle

Rates of intake of herbage and grazing time of beef cattle are essential components of simulation models of grassland agroecosystems. We studied the effects of herbage allowance on rates of intake and ingestive behaviour of twelve 2-year-old Angus heifers ( Bos taurus )(364 ± 12 kg) grazing pastures of tall fescue ( Festuca arundinacea Schreb.). A balanced change-over design and a novel tethering technique were used to estimate direct, residual and permanent effects of three herbage allowances on intake per bite, rate of biting and rate of intake. Herbage dry matter (D.M.) allowances, which were established by varying tether lengths, were 5, 9 and 13 kg (1·4, 2·5 and 3·6 kg/100 kg of live weight) and made available in circular plots of 15, 27 and 38 m 2 , respectively, for a single measured 2 h grazing session each day. Heifers grazing Kenhy tall fescue swards, composed of vegetative tillers and free from the endophyte Acremonium coenophialum , with herbage D.M. masses (> 5 cm) of 2000 kg/ha and D.M. allowances of 9 and 13 kg/2 h per heifer, ingested D.M. at 1·9 kg/h by taking bites averaging 800 mg D.M. at 38 bites/min. Allowances of 5 kg/2 h per heifer slowed the rate of intake to 1·3 kg/h by limiting D.M. intake per bite to 654 mg and biting rate to 35/min. Rate of D.M. intake of cattle grazing vegetative temperate grass swards appears to be ca. 0.5% of live weight per hour when allowance and availability of herbage are not limiting.

Moderation of grazing behavior of beef cattle by stable flies (Stomoxys calcitrans L.)

Abstract 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 (4 × 4) were used to evaluate the effects of stable flies on the behavior of Angus cows grazing vegetative tall fescue ( Festuca arundinacea Schreb. cv Johnstone) in screened enclosures. Four populations (0, 50, 100 and 150) of starved, laboratory-reared stable flies were released into each enclosure at 15 min intervals during 1 h grazing meals. Mean numbers of alighted stable flies increased linearly with treatment level up to 125 per animal and up to 46 on forelegs and up to 7 on hindlegs. Dorsal and ventral trunk surfaces each supported up to 35 alighted flies. Alighted fly numbers increased on all major body sectors as grazing meals progressed: when 150 stable flies were released, there were 25, 44, 56 and 63 flies on forelegs during successive quarters. Releases of up to 150 stable flies caused 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 swishes (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 (from 1.0–1.4 g) and a linear decline in rate of biting (from 41-35 bites min −1 ). Cows visited 3.2, 3.9, 4.3 and 3.4 feeding stations min −1 ingesting 16.1, 12.6, 10.9 and 16.0 g DM per feeding station when four pulses of 0, 50, 100 and 150 stable flies were released, respectively. Blood intake of engorged stable flies declined from 9.3 to 8.1 mg, either indicating competition between flies for feeding stations or deterrent actions of their hosts disturbed their feeding. Moderation of ingestive behavior of cows was attributed to annoyance of low populations of alighted flies. In the presence of stable flies, cattle may accelerate herbage intake and reduce grazing times.

Accessibility of Herbage Allowance and Ingestive Behavior of Beef Cattle

Rate of intake may be accelerated when grazing cattle (Bos taurus) are given access to fresh pasture. Two experiments using a balanced change-over design and tethered adult cows of 471±18 kg liveweight were used to measure the effect of accessibility of alfalfa (Medicago sativa L.) on ingestive behavior. In the first experiment, herbage dry matter (DM) allowances of 10.5 kg were available for 90 min in one, two or three equal portions by area and time. These treatments had little effect on ingestive behavior and cattle ate DM at a mean rate of 2.25 kg h−1 by taking bites of 1.5 g DM at 25 bites min−1. In a second experiment, cows had access to 8.8 kg herbage DM allowances as a whole (T1), in two equal portions (T2) in time and area within the same plot, or in two separate plots (T3). A mean rate of DM intake of 2.2 kg h−1 was attained by forming bites of 1.6 g at 23 bites min−1. Accessibility of allowance had no significant (P<0.05) effect on ingestive behavior. Rates of biting immediately before and after the change-over were 26 and 20, 17 and 33, and 16 and 28 for T1, T2, and T3, respectively. It was apparent that rates of biting accelerated when cows were exposed to fresh swards but the effects were transitory and contributed little to overall rates of DM intake.