Why is the COW considered holy in Hinduism?

The cow is a symbol of sacrifice. It eats grass, hay and Chaff-things that, we do not require, and in return, it gives us milk. The cow teaches us to be of use to others even while leading peaceful and humble life. We should take less and give to the society. That is why the cow is venerated as ‘Gho’ Mata

A lesson taught by the Cow.

Once in a slaughterhouse, a cow, when approached by the butcher, laughed at him. He was astonished and asked the cow, why it laughed at him even after knowing that he is going to kill it.

The cow answered, I haven’t consumed meat in my lifetime, I eat only grass and rotten vegetable that humans feed me. I haven’t rendered any harm to anyone. I have supplied milk to your children and your kins. The products (Ghee, butter) resulting from processing milk also is consumed by humans only. My Dung is used as fuel and as manure for your fields. I have been of immense help to you in all ways, but you have come to slaughter me. I have been nurturing be more than your mother, I have been the favourite of Lord Krishna. However, My death seems to be fierce. I have my lived my life in peace and have helped your kin to the best of my effort.  I am rendered a bad death, Now think about how bad your death is going to be. The butcher was moved to tears and left the cow unslaughtered. He hugged the cow and caressed it. The cow also was moved to tears.