Bell cow
The lead cow of a herd, wearing the bell that the others follow.
Also: lead cow, leader cow
A bell cow is a cow, usually experienced and calm, that leads the herd and wears its main bell, so that the others follow her sound and herders can track the group. Herds have a social order, and some cows naturally lead the way to water and pasture. In alpine processions the lead cow wears the largest bell and the finest headdress. In English the phrase is used figuratively, especially in American speech, for a person or business whose choices others follow, much like bellwether, which comes from the belled castrated ram that leads a flock of sheep.