This is the cow-mother. She is the source of fecundity and rich milk for all hoofed and horned creatures. Every farmer or herder calls her by whatever local animal he favors.
Eiritha is usually shown as a larger-than-life version of the popular local animal. Sometimes, especially among the Praxians, she is shown as a human-headed version of the beast, or as a beast-headed woman.
See Cult Compendium page 79