I have three Australorp hens I raised from chicks through laying age. They've been very healthy and beautiful and began laying nearly daily at 6 months. There was a fourth chicken that turned out to be a rooster. At 5 months, I took him back to the lady I got the chicks from and traded him for a Buff Orpington pullet about a month younger than my flock. The Buff has given my flock a respiratory illness. It has fortunately been mild, consisting of a week or so of coughing/sneezing without discharge. I have regretted getting the new pullet. Even though the illness seems mild and I may get lucky this time, I unwittingly violated some very important health rules for a flock. DO NOT introduce any new chickens! They call it the all-in, all-out rule. Raise your flock as one age group. I also violated another two rules.. no new breeds (even though Buff Orps and Australorps are from the same root stock,) and the age difference was a bad thing too. The lady doesn't have a very tidy operation and raises different ages and breeds all together. I should have been aware of several danger signs! DUH. I just hope I haven't done permanent damage to these beautiful hens.