The palatability of BFT varies with tannin concentration.
Tannins are very bitter, and are produced when the plant is stressed.
Some cultivars of BFT have naturally lower or higher ambient tannin concentrations. One disadvantage of using BFT for feed is that it may cause photosensitization in horses. Substitution value of birdsfoot trefoil for alfalfa-grass in pasture systems. Inheritance of condensed tannins in bird's-foot trefoil. Canadian Journal of Plant Science.