“Milking the cow means drawing the principles of religion in a liquid form. The great rsis and munis would live only on milk. Srila Sukadeva Gosvami would go to a householder while he was milking a cow, and he would simply take a little quantity of it for subsistence. Even fifty years ago, no one would deprive a sadhu of a quart or two of milk, and every householder would give milk like water.
For a Sanatanist (a follower of Vedic principles) it is the duty of every householder to have cows and bulls as household paraphernalia, not only for drinking milk, but also for deriving religious principles. The Sanatanist worships cows on religious principles and respects brahmanas. The cow’s milk is required for the sacrificial fire, and by performing sacrifices the householder can be happy. The cow’s calf not only is beautiful to look at, but also gives satisfaction to the cow, and so she delivers as much milk as possible.”
Srimad-Bhagavatam: Canto 1: “Creation”
by His Divine Grace A. C. Bhaktivedanta Swami Prabhupada