The sex-and-class label buyers care about, which depends on the species you picked:
Cattle: Steer, Heifer, Cow, Bull
Sheep: Lamb, Ewe, Ram, Wether
Goat: Kid, Doe, Buck, Wether
Hog: Barrow, Gilt, Sow, Boar
Horse: Gelding, Mare, Stallion
Mixed: for a pen group that isn't all one class
Required. It feeds how animals lot together and how the ring describes them, so pick the one that matches what's actually standing in the pen.