** I have written a similar answer before, I'm posting that content **

Our Vedas say that, all Gods themselves manifest in a Cow.

Why is a Cow given so much importance and considered sacred ?

• When a woman gives birth to a child, and due to some reasons, she is not able to feed her baby. Then the baby is fed cow’s milk, because the milk can be easily digestible for the new born. Thus, a Cow is given a mother's status.
• All living beings in order to survive, need water. And the only source of water is rain. Our ancestors, in order to please Gods, performed Yagnas (Varuna yagna for rain). And yagnas can't be performed without Cow ghee. Thus Cows are our saviours, in whose absence all the living beings cease to exist.
• Encircling the Cow along with its new born calf and a Shivling, is equivalent to encircling the entire world.
• Performing prayer to cow daily, will free you from few sins.
• They sprinkle Gomuthrum (cow urine) in the entire house (to get rid of negative energies).
• Lord Krishna has said in Bhagavadgita, “ I manifest in every living being and among cows I'm the Kamadhenu”.