Krsna had many thousands of cows, and they were divided into groups according to their colors. They were also differently named according to color. When He would prepare to return from the pasturing ground, He would gather all the cows. As Vaisnavas count 108 beads, which represent the 108 individual gopis, so Krsna would also count on 108 beads to count the different groups of cows.
From Srila Prabhupada’s Krsna Book ch. 35: The Gopis’ Feelings of Separation