The R.C.R.I.R. was NOT vaccinated for Mericks. Others supposedly were. ? They came from a small hobby farm. Chickens do drink out of dirty mud puddles where the horses are when they free range. So far my the older hens, different flock, (they came from the feed store), about 1 1/2 yr. old seem okay. It is only the 7mo. old ones form the hobby farm are dieing. ? ? ?