Like hormones, Australian chickens are not given steroids in any way. Their size occurs naturally due to selective breeding and optimal nutrition. Steroids and hormones haven’t been used in the chicken meat industry for more than 60 years.
Meat chickens have been selectively bred over the past 60 years for a variety of characteristics, including growth rate and efficiency to convert feed into meat. This is why they reach the desired market weight and quality more quickly than the progenitor breeds of chickens from which they were originally derived.
A key reason for people thinking steroids, like hormones, are in chicken may be that the chickens sold these days in supermarkets, butcher shops and chicken shops are much bigger than what they may recall them to have been 20, 30 or 40 years ago, and it may be easy to conclude that this must be the result of some unnatural intervention.