329. Purified Flavonoids Alter Vascular Hemodynamics Alleviating Fescue Toxicosis in Sheep.

Abstract Research has consistently demonstrated that supplementation with flavonoid containing legumes (red clover, white clover, and soybean) can reverse vasoconstriction, improve growth, and impart thermotolerance in ruminants challenged with fescue toxicosis. Despite the consistent vascular benefits observed, legume sources vary in flavonoid concentration and composition and the impact of individual flavonoids on arterial hemodynamics has not been previously evaluated in ruminants. Therefore, the objective of this research was to determine the vasoactivity and potential benefits of the purified isoflavones biochanin A (BCA) and formononetin (FORM) and the flavones luteolin (LUT) and apigenin (API) in sheep subjected to a fescue toxicosis challenge. Nine mature, ruminally cannulated Polypay wethers (87.6±2.6-kg) were first adapted to the basal diet (85% orchard grass pellets, 15% concentrate mix) ad libitum for 3-wk. Animals were then moved to individual climate-controlled pens (cyclical environmental conditions; high temperature-humidity-index [THI]:80.4, low THI:69.3) and underwent two, 9-d experiments each consisting of a 2-d baseline and a 7-d fescue toxicosis challenge, separated by a 7-d washout. For both experiments, animals were stratified by weight and randomly assigned to one of three treatments: an endophyte-infected tall fescue (E+TF) seed only control (CON) in both experiments and then either E+ TF seed + BCA or FORM (isoflavone experiment) or E+ TF seed + LUT or API (flavone experiment). During each challenge period, all flavonoid treatments were provided at a rate of 0.5 mg/kg BW and were dosed through the ruminal cannula with E+ TF seed (15 µg/kg BW ergovaline + ergovalanine) daily prior to feeding (0730-h). Carotid artery hemodynamics, rectal temperatures, and respiration rates were collected at baseline (ultrasound only) and on days 5 to 7 of the fescue toxicosis challenge period at 1200-h. Ultrasound data were analyzed as proportionate differences (PDIFF) from baseline measures using the following equation: PDIFF = [(treatment − baseline) ÷ baseline] × 100. All data were analyzed by repeated measures using the MIXED procedure of SAS (v.9.4). Dry matter and water intake were unaffected by treatment (P > 0.11). In both experiments, carotid artery luminal areas (-28% to -50%) and blood flow rates (-18% to -25%) were below baseline in CON wethers, indicative of vasoconstriction (P ≤ 0.05). All isoflavone and flavonoid treatments resulted in greater carotid artery luminal areas (+45 to + 63%) and blood flow rates (+60% to + 350%) relative to CON (P ≤ 0.05). Rectal temperature was unaffected by treatment (P > 0.82), but all purified flavonoids tended to have lower respiration rates (102 to 120 breaths/min) than CON (130 to 141 breaths/min; P ≤ 0.08). In conclusion, supplementation with the isoflavones BCA and FORM and flavones LUT and API resulted in vasodilation above baseline and decreased respiration rate with fescue toxicosis challenge, indicating potential for improving thermotolerance.