In India, the cow is worshipped like no other symbol and is considered to be sacred and like a mother-figure. The cow is considered sacred due to the following reasons:
1.  The cow was regarded as one’s mother as it sacrificed the milk meant for its calf and provided milk for the people.  It is therefore a symbol of a 'mother' in India
2.  The cow was also kept at many Indian homes for its milk, its good nature and the animal became a part of the family.
3.  At the beginning of the Epic period (c.l000- 800 BC), cow’s meat was said to be common food that added vigor not only to the body but also to the mind. A theory suggests that during the 5th century it was discovered that the cattle population was decreasing at an alarming rate. People began to realize that a live cow was a greater asset than its meat.
4.  Ghee, milk and yogurt were vital for temple rituals, this animal began to enjoy a greater value alive.
5.  In the Atharvaveda (vedic text) beef-eating was prohibited as it was likened to committing a sin against one's ancestors.
6.  Other factors that contributed to the rise of vegetarianism in India was that kings such as Ashoka (c. 322-183 13C) discouraged the killing of all animals. The powerful turned benevolent  Emperor Ashoka of that time popularized a vegetarian cuisine. Even today a majority of Indians are vegetarian.
7.  The two other individuals that helped make India vegetarian are Mahavir and Buddha who were India's regional kings turned spiritual teachers. (Also the ancient, urban Dravidian civilization may have been vegetarian.)
This was the start of the taboo of eating beef in India.