We really don't pray to cows.  We respect, and when we greatly respect out of love, we call it worship. Worshiping means paying particular attention, care and concern.

We worship cows, we worship people, we worship our mother because we simply respect them all. We sincerely love them. We don't want to hurt them.

India, being an agriculture society in its early days, found the cow useful not only for milk but also for plowing the land and for transportation. The cow was very important to the Aryans, so they gave more importance to cows than the other creatures.  Like you are more important to your parents than other people so they serve you more. So to respect cow is just like we respect automobile today. We care for the cars because it is a necessity. So instead of word "care", we might use the word "prayer" or "worship." 

Hence the cow is considered a manifestation of God. It represents all the helpless animals that cannot talk. By respecting them it means we should not take advantage or harm them, but be lovable to all creatures.

Worshiping does not mean that they have become God, but that God has manifested in them. To worship a cow means to worship all the helpless ones including the sick, poor, and old. The life of a worldly person will show that he is always worshiping where he finds himself as a benefactor; it is a selfish attitude. He will worship all that he has --  a house, a car, or money. To make more money some will want to study more; they will become doctors to make more money rather than to serve mankind.

There is nothing wrong in respecting or worshiping all creatures, including cows. We should really be worshiping the entire universe as the Gita teaches us. To worship means to respect, to love, and to dignify everything --  including ourselves.

-- Swami Radhanandaji