Lord Krsna, as the teacher of human society, personally showed by His acts that the mercantile community, or the vaisyas, should herd cows and bulls and thus give protection to the valuable animals. According to smrti regulation, the cow is the mother and the bull the father of the human being. The cow is the mother because just as one sucks the breast of one’s mother, human society takes cow’s milk. Similarly, the bull is the father of human society because the father earns for the children just as the bull tills the ground to produce food grains. Human society will kill its spirit of life by killing the father and the mother. It is mentioned herein that the beautiful cows and bulls were of various checkered colors — red, black, green, yellow, ash, etc. And because of their colors and healthy smiling features, the atmosphere was enlivening.

From Srila Prabhupada’s purport to SB 3.2.29