Why do Indian brides enter the bedroom with a glass of milk for the groom on the day of consummation ( Suhagraat ) ?

Generally the milk that is given to the groom by the bride has haldi (turmeric) or kesar (saffron) mixed in it. 

Both these ingredients are known to be aphrodisiacs.

An aphrodisiac is a substance that increases sexual desire on consumption.

Thus the milk with haldi or kesar is given to arouse or intensify the sexual desire of the groom, since its the wedding night ;).

When the bride comes in with the milk is it for her or for the man. As far as energy is concerned a glass of milk has approximately 237 calories (Milk, indian buffalo, fluid) and energy consumed during sex is approximately 33 calories per hour. So ideally the glass of milk shared between the two should sustain activity for 4 hours. When, that must be exhausting on all the senses!

As we know Ancient Indians were farmers. They gave lot of importance to cattle farming since it gives a wide range of products varying from cow dung to ghee. These things were considered as auspicious because it had an important role in their daily life. They could relay on milk and related products to survive for a long time. So cattle became the symbol of the wealth during the ancient times, so that the milk, the major product.

So when the bride enter the bedroom with milk in her hand, it symbolizes the wealth, a good fortune she brings to one's life. 

This also showcase the sweetness of the upcoming life. As the bride and groom said after the "Saptapadi"

"May the night be honey-sweet for us. May the morning be honey-sweet for us. May the earth be honey-sweet for us. May the heavens be honey-sweet for us. May the plants be honey-sweet for us. May the sun be all honey for us. May the cows yield us honey-sweet milk."

source:- quora.com