Calculus bovis

Calculus bovis, niu-huang (牛黃) or ox bezoars are dried gallstones of cattle used in Chinese herbology. In Asian countries calculus bovis are harvested when cattle (Bos taurus domesticus Gmelin) are slaughtered. Their gall bladders are taken out, the bile is filtered, and the stones are cleaned and dried. In western countries they are usually discarded.

Calculus bovis have a color varying from golden yellow to brownish yellow. The shape of a stone is variable and depends on how it was formed, becoming spherical, oval, triangular, tubular or irregular.

Since natural calculus bovis are scarce they can be very expensive. There are artificial calculus bovis used as substitutes. These are manufactured from cholic acid derived from bovine bile.