Location: Forage-animal Production ResearchTitle: Mitigation of ergot vasoconstriction by clover isoflavones in goats (Capra hircus)
|HUIHUA, JI - University Of Kentucky|
|BUSH, LOWELL - University Of Kentucky|
Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2016
Publication Date: 3/4/2016
Citation: Aiken, G.E., Flythe, M.D., Kagan, I., Huihua, J., Bush, L.P. 2016. Mitigation of ergot vasoconstriction by clover isoflavones in goats (Capra hircus). Frontiers in Veterinary Science. doi: 10.3389/fvets.2016.00017.
Interpretive Summary: Tall fescue is a cool-season perennial grass that is utilized as a forage on approximately 15 million hectares in the eastern half of the USA. The grass is productive and tolerant of environmental stresses, which has been attributed to presence of a fungal endophyte that infects most plants of tall fescue. However, ergot alkaloid toxins are also produced by the endophyte, which cause a toxicosis in grazing livestock. Signs of ‘fescue toxicosis’ include poor weight gain and reproductive performances, elevated body temperature, and labored respiration. Elevated core body temperatures in animals exposed to ergot alkaloids is known to be caused by constriction of blood flow to peripheral tissues in response to ergot alkaloid exposure. There is evidence that isoflavones produced by legume plants can relax the vasculature to relieve alkaloid-induced vasoconstriction. Results from pen experiments that evaluated vasculature responses of goats to ergot alkaloids and the isoflavone, biochanin A, produced by clovers, determined that biochanin A can relieve alkaloid-induced vasoconstriction during and after exposure to ergot alkaloids. This provides evidence that over seeding toxic endophyte-infected tall fescue with clovers can relieve ergot alkaloid-induced constriction of blood flow to peripheral tissues and, therefore, reduce the vulnerability of severe heat stress that is suffered by livestock exposed to the toxins. These results will be of interest to the numerous livestock producers interested in technologies that can alleviate or mitigate the adverse effects of fescue toxicosis.
Technical Abstract: Ergot alkaloids produced by a fungal endophyte (Epichloë coenophiala; formerly Neotyphodium coenphialum) that infects tall fescue (Lolium arundinaceum) can induce persistent constriction of the vasculature in ruminants, hindering their capability to thermo-regulate core body temperature. There is evidence that isoflavones produced by legumes can relax the vasculature, which suggests the possibility they could relieve alkaloid-induced vasoconstriction. Two pen experiments were conducted with rumen fistulated goats (Capra hircus) to determine with ultrasonography if isoflavones can 1) promote vascular compliance by countering alkaloid-induced vasoconstriction, and 2) relieve already imposed alkaloid-induced vasoconstriction. Goats were fed ad libitum chopped orchardgrass (Dactylis glomerata) - timothy (Phleum pratense) hay prior to conducting the experiments. Baseline measures of carotid and interosseous luminal areas were obtained with goats on hay without infusions, and for blood flow rate in the carotid artery in Exp. 2. Responses to infusion treatments were evaluated as proportionate differences from baseline measures. Peak systolic velocity, pulsatility index, and heart rate were measured on the last day of treatment (DOT) in Exp. 1, and on all imaging sessions during Exp. 2. For Exp. 1, rumens were infused with ground toxic fescue seed and isoflavones in Phase A and with only the toxic seed in Phase B. The infusion treatments were switched between phases in Exp. 2, which employed a fescue seed extract having an ergot alkaloid composition equivalent to that of the ground seed used in Exp. 1. During Exp. 1, luminal areas of carotid and interosseous arteries in Phase A did not deviate (P > 0.1) from baselines over 1, 2, 3, and 4 DOT, but the areas of both declined linearly from baselines over 1, 2, 3, and 4 DOT in Phase B. By 6, 7, and 8 DOT in Exp. 2, luminal areas of the arteries and flow rate declined from baselines with infusions with the only seed extract in Phase A, but luminal areas and flow rate increased over 4, 5, and 6 DOT with the additional infusion of isoflavones. Peak systolic velocity and heart rate were not affected by treatment in either experiment, but were highest when infused with only ergot alkaloids in both experiments. Results indicate that isoflavones can relax persistent vasoconstriction in goats caused by consumption of ergot alkaloids.