Submitted to: Frontiers in Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2014
Publication Date: 11/20/2014
Citation: Aiken, G.E., Flythe, M.D. 2014. Vasoconstrictive responses by the carotid and auricular arteries in goats to ergot alkaloid exposure. Frontiers in Chemistry. 2:101. DOI: 10.3389/fchem.2014.00101.
Interpretive Summary: Tall fescue is a cool-season perennial grass that serves as the predominant forage utilized for forage-based livestock production in the upper U.S. transition zone, between the temperate northeast and the subtropical southeast. A fungal endophyte infects most plants of tall fescue produces alkaloids that impart the plant with tolerances to dry weather and heavy grazing. Unfortunately, the endophyte also produces ergot alkaloids that cause a toxicosis in grazing animals. Cattle exhibiting signs of toxicosis will maintain rough hair coats through the summer monthes, have low prolactin concentrations, and be vulnerable to heat stress. Ergot alkaloids induce persistent vasoconstriction of blood flow to peripheral tissues that can restrict the animal’s ability to regulate core temperature. Consequently, cattle will spend more time under shade and standing in ponds than they will grazing. Vasconstrictive responses have been reported in cattle, horses, and sheep, but not in goats. A pen study used color Doppler ultrasonography to compare luminal areas in rumen fistulated wether goat that were fed orchardgrass hay and infused with either endophyte-infected or non-infected tall fescue. Luminal areas of the carotid and auricular arteries decreased approximately 40% after they were infused with endophyte-infected seed. Goats grazed on tall fescue are susceptible to alkaloid-induced vasoconstriction, but more research is needed to determine this vulnerability in pastures with diverse grass and broadleaf mixtures that are typically maintained for goat pastures.
Technical Abstract: A fungal endophyte (Neotyphodium coenophialum) infects most plants of ‘Kentucky 31’ tall fescue (Lolium arundinaceum) and produces ergot alkaloids that cause persistent constriction of the vascular system in grazing livestock. Consequently, animals undergoing this toxicosis cannot regulate core body temperature and are vulnerable to heat and cold stresses. An experiment was conducted to determine if the caudal and auricular arteries in goats (Capra aegagrus hircus) vasoconstrict in response to ergot alkaloids. Seven, rumen fistulated goats were fed ad libitum orchardgrass (Dactylis glomeratia) hay and ruminally infused with endophtye-free seed (E-) for a 7-day adjustment period. Two periods followed with E- and endophyte-infected (E+) seed being randomly assigned to the 2 goat groups in period 1 and then switching treatments between groups in period 2. Infused E+ and E- seed were in equal proportions to the hay such that concentrations of ergovaline and ergovalanine were 0.80 µg per g dry matter for the E+ treatment. Cross-sections of both arteries were imaged using color Doppler ultrasonography on days 0, 2, 4, 6, 8, and 12 in period 1 and on days 0, 1, 2, 3, 6, 7, and 9 in period 2. Differences from average baseline areas were used to determine presence or absence of alkaloid-induced vasoconstriction. Carotid arteries initiated constriction on imaging day 2 in both periods, and auricular arteries initiated constriction on imaging day 2 in period 1 and on day 6 in period 2. Luminal areas of the carotid arteries in E+ goats were 46% less than baseline areas in both periods after vasoconstriction occurred, whereas auricular arteries in E+ goats were 52% less than baseline areas in period 1 and 38% in period 2. Both arteries in E+ goats in period 1 relaxed relative to baseline areas by imaging day 2 after they were switched to the E- treatment. Results indicated that goats exhibit a vasoconstrictive response to ergot alkaloids that could disrupt thermoregulate their core body temperatures.