During Kaarthika month, the first day after Diwali/Deepavali is called Sudha Padyami. On this special day, people perform puja for cows.
Cow is considered a sacred symbol even in ancient India as well as in parts of Europe. Cow provides various sources of food and it was considered very foolish to eat the animal which provides much more than meat. (Remember the story of the naive fool who killed the Duck that produced one golden egg per day?).