Why cow races are held on Govardhan Puja in a Rajasthan village?

In a unique tradition, Vasa village in Rajasthan's Sirohi organises cow races during Govardhan Puja. According to the villagers, if the nilgai (blue bull) wins the race, the new year is supposed to be auspicious. A white cow's victory predicts moderate rainfall and a good harvest, while a black cow's victory is predicted to bring scanty rainfall or famine.