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ANIMAL PRODUCTION |
* USDA-ARS, Forage-Animal Production Research Unit, Lexington, KY 40546;
and
USDA-ARS, Dale Bumpers Small Farms Research Center, Booneville, AR 72927;
and
University of Kentucky, Lexington 40546; and
University of Tennessee, Knoxville 37996-4574
2 Corresponding author: glen.aiken{at}ars.usda.gov
Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) noninfected (E–, 0 µg of ergovaline/g of DM), a 1:1 mixture of endophyte-infected and E– (E+E–; 0.39 µg of ergovaline/g of DM), or endophyte-infected (E+, 0.79 µg of ergovaline/g of DM) tall fescue (Lolium arundinaceum) seed. Eighteen crossbred (Angus x Brangus) heifers [345 ± 19 kg (SD)] were assigned to individual pens and fed chopped alfalfa hay plus a concentrate that contained E– tall fescue seed for 7 d during an adjustment period. A 9-d experimental period followed with feeding treatments of chopped alfalfa hay plus a concentrate with E+, E–, or E+E– seed being assigned randomly to pens. Doppler ultrasound measurements (caudal artery luminal area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, and flow rate) and serum prolactin were monitored during the adjustment (3 baseline measures) and during the experimental period (7 measures). Statistical analyses compared proportionate differences between baseline and responses at 3, 27, 51, 75, 171, and 195 h from initial feeding of the experimental diets. Serum prolactin concentrations for E+ and E+E– diets were less (P < 0.001) than baseline concentrations beginning at 27 and 51 h, respectively, from initial feeding of the diets. Although baseline measures were taken when ambient temperatures were likely below thermoneutrality, caudal artery luminal cross-sectional area in E+ heifers had declined (P = 0.004) from baseline by 27 h and remained less (P < 0.02) until 195 h, and caudal artery luminal area declined (P = 0.004) in E+E– heifers from baseline by 51 h and remained less (P < 0.07) until 171 h. Blood flow rate was slower than the baseline rate at 51 h for E+ (P = 0.058) and E+E– (P = 0.02 heifers, but blood flow remained slower in E+E– heifers for 48 h, whereas it remained slower in E+ heifers for 96 h. Adjustments in artery luminal area and blood rate with the 3 diets appeared to parallel the increases in ambient temperature. Heifers fed a diet containing a larger amount of ergot alkaloids had less of a response to ambient temperature than heifers consuming the diet with less or no ergot alkaloids.
Key Words: beef cattle • Doppler ultrasonography • fescue toxicosis • Lolium arundinaceum • tall fescue • vasoconstriction
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