Isoflavone rumen metabolites: A missing link in the benefits of legumes on grazing animal production

Authors: Flythe, Michael; Aiken, Glen; Kagan, Isabelle

Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/4/2015
Publication Date: 1/12/2016
Citation: Flythe, M.D., Aiken, G.E., Kagan, I. 2016. Isoflavone rumen metabolites: A missing link in the benefits of legumes on grazing animal production. American Forage and Grassland Conference Proceedings. Pg. 13.

Interpretive Summary:

Technical Abstract: Clovers are widely used to add protein to ruminant diets. Clovers and other legumes also produce a class of small molecules called isoflavones. Isoflavones have estrogenic properties, which can interfere with reproduction in grazing ruminants, but they also have benefits. We identified potential benefits of clover isoflavones for grazing animals, including improvements in rumen function and relaxation of blood vessels. In laboratory tests, red clover (Trifolium pratense) extracts decreased amino acid degradation by rumen bacteria. The active component in the extracts was an isoflavone, biochanin A, which inhibited the same group of amino acid-degrading bacteria as ionophore antibiotics. The results of feeding trials supported the idea that biochanin A could increase weight gain, as do growth-promoting antibiotics. The spring and fall trials involved grazing steers that were or were not supplemented with dried distillers’ grains with and without biochanin A (mixed with the grains to a level commensurate with a 33% red clover diet). Average daily gain was greater in the groups that received biochanin A. Additionally, rumen bacteria metabolize isoflavones, and some of those metabolites are known to dilate blood vessels. Vasodilation would be beneficial because many ruminants are exposed to ergot alkaloids that cause chronic vasoconstriction (i.e. fescue toxicosis). Goats were administered toxic tall fescue and red clover extracts, and two arteries in each goat were observed with ultrasonography. The clover extract decreased vasoconstriction caused by the tall fescue extract. These results may explain many of the benefits seen in animals grazing clovers.