Hemodynamic responses of the caudal artery to toxic tall fescue in beef heifers

¹ USDA-ARS, Forage-Animal Production Research Unit, Lexington, KY 40546
² University of Kentucky, Lexington, KY 40546
³ USDA-ARS, Dale Bumpers Small Farms Research Center, Booneville, AR 72927
⁴ University of Tennessee, Knoxville, TN 37996-4574

^* To whom correspondence should be addressed. E-mail: geaiken{at}ars.usda.gov.

	Abstract

Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with either endophyte (Neotyphodium coenophialum) infected (E+) or non-infected (E-) tall fescue seed. Eighteen crossbred (Angus x Brangus) heifers were assigned to 6 pens and were fed chopped alfalfa hay for 5 d and chopped alfalfa hay plus a concentrate that contained E- tall fescue seed for 9 d during an adjustment period. An 11-d experimental period followed with animals in 3 pens fed chopped alfalfa hay plus a concentrate with E+ seed and those in the other 3 pens were fed chopped hay plus concentrate with E- seed. Doppler ultrasound measurements (caudal artery area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, stroke volume, and flow rate) and serum prolactin were monitored during the adjustment (baseline measures) and during the experimental period. Three baseline measures were collected on d 3, 5, and 6 during the adjustment period for comparison to post E+ seed exposure. Statistical analyses compared proportionate differences between baseline and response at 4, 28, 52, 76, 100, 172, and 268 h from initial feeding of E+ seed. Serum prolactin concentrations on both diets were lower (P < 0.001) than baseline beginning at 4 h from the start of the experimental period. However, trends in serum prolactin concentrations for heifers on the E- diet suggested ambient temperature was affecting these concentrations. Caudal artery area in E+ heifers had declined (P < 0.10) from baseline by 4 h and was consistently lower (P < 0.05) for the remainder of the period. Heart rates for E+ heifers were lower than the baseline rate from 4 (P < 0.10) to 100 (P < 0.001) h, but were similar (P > 0.10) to the baseline for 172 and 268 h measures. Blood flow in E+ heifers was consistently lower than the baseline from 4 (P < 0.05) to 172 (P < 0.001) h, but was similar to the baseline at 268 h when heart rate was similar to the baseline rate. Caudal artery areas for the E- diet were similar to baseline areas except at 100 h when it was greater than baseline. Heart rates and flow rates for E- heifers did not differ (P > 0.10) from baseline measures during the experimental period. Results indicated that onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.

Key Words: beef cattle, tall fescue , Schedonorus arundinaceus, fescue toxicosis, Doppler ultrasonography, vasoconstriction

This article has been cited by other articles:

				J. L. Klotz, B. H. Kirch, G. E. Aiken, L. P. Bush, and J. R. Strickland Bioaccumulation of ergovaline in bovine lateral saphenous veins in vitro J Anim Sci, July 1, 2009; 87(7): 2437 - 2447. [Abstract] [Full Text] [PDF]

				G. E. Aiken, J. R. Strickland, M. L. Looper, L. P. Bush, and F. N. Schrick Hemodynamics are altered in the caudal artery of beef heifers fed different ergot alkaloid concentrations J Anim Sci, June 1, 2009; 87(6): 2142 - 2150. [Abstract] [Full Text] [PDF]

				G. E. Aiken, J. L. Klotz, B. H. Kirch, J. R. Strickland, and D. L. Boykin Technical note: Comparison between two tracing methods with ultrasonography to determine lumen area of the caudal artery in beef cattle J Anim Sci, January 1, 2009; 87(1): 371 - 374. [Abstract] [Full Text] [PDF]