In Hindu mythology, Nandini is the offspring of Surabhi, the cow of plenty who in different tales belongs to various people, including the sage Vasishtha. She is capable of offering many blessings, including (predictably) fertility. She is one of those objects that recur in mythology as something to be guarded, cared for, or stolen.
Cows are constant company to Krishna, and Nandini is counted among his favorites.