Hello sir,
To open dairy you need a land for cultivating fodder, water for dairy , capital, shed .
ruffly it requires 1 lakh is required to maintain one cow of good breed even you can start with small one also with less investment.
department of animal husbandary provides subsidy for the investment you made. you can decide no of cows based on your investment then prepare a project and submit to your bank they will approve as dairy is one of the profitable venture.
maintenance of cow hyggine condition has to be maintain. if you are new to this field do under go some training then have your venture started.