Having tried it both ways, I've found that it works best for me to integrate between 3 and 6 weeks old. If they are integrated while they are younger, and smaller, they are not considered to be much of a threat to the pecking order. Pretty much, they might get an obligatory peck if they get under foot... otherwise, they're ignored.I've heard and have had good luck with waiting until the chicks stop peeping and are making adult sounds instead.