I am raiseing holstein calves and have run into alot of problems with pneumonia. I have given them shots of nuflor, micotil,and have a high level of aureomycin in the feed. It seems that they get alittle better and look good for awhile then get sick again. My vet just keeps giving med. for them but it doesn't stop the problem. These calves are about 8 weeks old and are off of milk. They are eating pretty well most of the time. I have them in a barn that isn't closed up to much and they have to go outside to drink. Do you have any suggestions for this problem?