Vasoconstrictive Responses of the Carotid Artery in Pregnant Ewes to Ergot Alkaloid Exposure

Color Doppler ultrasonography was used to assess ergot alkaloid-induced vasoconstriction in pregnant ewes (Ovis aries) that were fed diets with or without toxic endophyte-infected seed of tall fescue (Lolium arundinaceum). A fungal endophyte (Epicloë coenophialia)that infects most plants of the standard cultivar of tall fescue, ‘Kentucky 31,’ produces ergot alkaloids that can cause a persistent constriction of blood flow in grazing ruminants, which incapacitates the animal’s ability to thermo-regulate core body temperature. Suffolk ewes were stratified by BCS for random assignment to four treatment groups (n = 15/treatment). Either endophyte-free (E-) or endophyte-infected (E+) tall fescue seed were fed in similar diet concentrations such that the daily consumption of ergovaline and ergovalanine for E+ was 1772 µg/ewe/d mixed in a TMR (corn, soybean meal, and cottonseed hulls). The ewes were fed the TMR without seed for the first 35 d. On day 35, ewes were fed endophyte-free (E-) or endophyte-infected (E+) seed, and on day 86, half of each group was switched to the opposite treatment (E-E+ or E+E-) and half remained on the same treatment (E-E- or E+E+ ) to parturition. Ultrasound imaging of left carotid artery was done at the start of lambing and the range in days on fed seed ranged from 50 to 106 days. Color Doppler ultrasonography was performed using a Classic Medical TeraVet 3000 Ultrasound Unit (Classic Universal Ultrasound, Tequesta, FL) with a 12L5-VET (12 MHz) linear array transducer. Cross-sectional area of the left carotid artery was measured for each ewe to determine luminal area, and a Power Doppler image was collected for measuring peak systolic and end diastolic velocities, heart rate, and pulsatility and resistance indices. Luminal areas were similar (P > 0.5) between E-E- (28.8 ± 1.98 mm²) and E+E- (30 ± 1/85 mm²) treatments, and between E+E+ (17.0 ± 2.06 mm²) and E-E+ (17.5 ± 2.06 mm²). Carotid arteries with E-E- and E+E- treatments were relaxed (P < 0.001) in comparison to those with the E+E+ and E-E+ treatments. Although there were no treatment effects (P > 0.10) on peak systolic and end diastolic velocities or heart rate, pulsatility and resistance indices were greater (P < 0.05) for E+E+ and E-E+ than for E-E- and E+E- treatments. Results indicated a vasoconstrictive response of the carotid arteries in pregnant ewes exposed to ergot alkaloids, but vascular recovery was demonstrated for sheep that had been switched from E+ to E- diets.