I have an ongoing cough in my flock of silkies .Its a quick high pitched cough.Two different times I have given tetracycline for 14 days,2 tsp per gallon of water fresh everyday.I noticed today that one is sneezing.This time of year the coop is very dusty and it has been extremely cold here,they do have heat at night so the coop never gets lower than 28 degrees.Is there something else that I can give them that could be put in the water or food,?I have 40.Thanks for any help