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UNDERRUN HEELS: The slope of the heels is shallower than that of the toe as viewed from the side. This reduces the posterior support of the hoof. Heels need not be short to be underrun. a.k.a: Run-under heels; underslung heels.
UNDERSLUNG HEELS: See: Underrun heels.
UNILATERAL: On one side only.
UNSOUND: Describes a horse who suffers from a defect or condition which could lead to lameness. An unsound horse might not be currently lame.
URINE: Average 5.5 quarts per day (3 to 9 range), deep yellow to brown color.