The biggest problem in a dairy is not as much what they eat but they go to bathroom in feed and the cows get sick and get antibiotics and we ingest this buying dairy , but yes i speak to some farmers here who estimate 25k yr in losses from them , also the farm ones good eating but city birds are not .like city pigeons which eat anything , this is true with anything I guess where I live eating a river mallard duck is good same duck in ocean is horrible I think because they eating shell fish with sea water possibly , so I guess environment matters .