Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2007
Publication Date: 9/1/2007
Citation: Aiken, G.E., Kirch, B.H., Strickland, J.R., Bush, L.P., Looper, M.L., Schrick, N.F. 2007. Hemodynamic Responses of the Caudal Artery to Toxic Tall Fescue in Beef Heifers. Journal of Animal Science. 2007. 85:2337-2345. Interpretive Summary: Tall fescue is a cool-season perennial grass that covers approximately 35 million ha in the eastern USA. An endophytic fungus is found in plants greater than 90% of tall fescue pastures and produces alkaloid toxins that induce the fescue toxicosis malady. Toxicosis has symptoms that include retention of rough hair coat, elevated body temperature, labored respiration, and decreased serum prolactin. Toxicosis and the adverse effects of the toxins on reproductive performance cost the livestock industry approximately 1 billion dollars per year. A research project using Doppler ultrasonography showed that blood flow of cattle can be altered within 4 hours of consuming ergot alkaloids. These findings indicated the sensitivity that cattle have to ergot alkaloids. It was also shown that Doppler ultrasonography has potential use as a non-invasive research tool for investigating the effects of ergot alkaloids on vascular circulation. This research provides information to all cattlemen in the fescue belt (region west ot the Great Plains and between the temperate northeast and subtropical southeast) on the sensitivity of their cattle to the fescue toxins and evidence of concern even with short-term grazing of endophyte-infected tall fescue.
Technical 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 six 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 three 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 percent 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 levels 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 shown to be similar to the baseline rate. Caudal artery areas for the E- diet were similar to baseline areas except at 100 h when it was higher than baseline. Heart rates and flow rates for E- heifers did not differ from baseline measures during the experimental period. Results of the experiment indicated that the onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.