what should be the ideal milk production to buy a desi cow

For a desi dairy cow, a good buying target is around six to ten liters per day. A very well managed Gir or Sahiwal can give more, but check the milk in your presence and see which month of lactation she is in. Peak milk is in month two to three, then it falls. If you want steady supply, buy a cow in second or third lactation, not an old one. Consult a veterinarian before administering any medicine or treatment.