Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2009
Publication Date: 6/1/2009
Citation: Aiken, G.E., Strickland, J.R., Looper, M.L., Bush, L.P., Schrick, F.N. 2009. Hemodynamics are Altered in the Caudal Artery of Beef Heifers Fed Different Ergot Alkaloid Concentrations. J. Anim Sci..2009; 87: 2142-2150
Interpretive Summary: Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with either endophyte (Neotyphodium coenophialum) non-infected (E-, 0 µg ergovaline/g DM), a 1:1 mixture of endophyte-infected and E- (E+E-; 0.39 µg ergovaline/g DM), or endophyte-infected (E+, 0.79 µg ergovaline/g DM) tall fescue seed. Eighteen crossbred heifers 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 either E+, E-, E+E- seed being randomly assigned to pens. Doppler ultrasound measurements (caudal artery 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 lower (P < 0.001) than baseline concentrations beginning at 27 and 51h, respectively, from initial feeding of the diets. Caudal artery area in E+ heifers had declined (P < 0.10) from baseline by 27 h and remained lower (P < 0.05) until 195 h, and caudal artery area declined in E+E- heifers from baseline by 51 h and remained lower (P < 0.10) until 171 h. Blood flow rate was lower (P < 0.10) than the baseline rate by 51 h for E+ and E+E- heifers, but blood flow remained lower in E+E- heifers for 48 h, whereas it remained lower in E+ heifers for 96 h. Adjustments in artery areas and blood rates with the 3 diets appeared to coincide with increases in ambient temperature. Results indicated that blood flows in cattle are reduced with consumption of diets that contain either 0.39 or 0.79 0 µg ergovaline/g DM, but vascular adjustment to changes in ambient temperatures was more rapid with consumption of the diet that had lesser ergot alkaloid concentrations.
Technical Abstract: Tall fescue is a cool-season perennial grass that is widely utilized for grazing in a region covering the transition zone between the temperate northeast and the subtropical southeast Although tall fescue is well adapted to the climate and soils in the region, an endophytic fungus infects fescue plants that produces ergot alkaloids, which can induce vascular constriction to restrict the animal’s ability to effectively dissipate body heat. Constricted blood flow to peripheral tissues can lead to severe hyperthermia in warm ambient temperatures and hypothermia in cold ambient temperatures. Vasoconstriction is part of a complex of symptoms for a toxicosis inflicted on cattle that graze endophyte-infested tall fescue. Toxicosis annually costs the cattle industry upwards of 1 billion dollars. A threshold concentration of ergot alkaloids in the diet needed to elicit a vasoconstriction response has not been documented. Therefore, an experiment was conducted to evaluate the blood flow characteristics in the caudal arteries of heifers fed diets containing 0, 0.39, or 0.79 mg ergovaline/kg DM. The caudal artery supplies oxygenated blood to the tail. Results of the experiment indicated a vasoconstriction response in 27 h following initiation of a diet that contained 0.79 µg ergovaline/g DM, and in 51 h following initiation of diet that contained 0.39 µg ergovaline/g DM. Although declines in blood flow rates were detected at 51 h for both experimental diets. Blood flow in cattle clearly was sensitive with the low concentrations of ergovaline fed in the experiment. Further, altered blood flow can occur with short-term grazing of endophyte-infected tall fescue. This information is critical to extension specialists/agents and producers who are challenged to develop management strategies with endophyte-infected tall fescue that minimize the effects of fescue toxicosis and altered blood flow on cattle performance.