Scott, I hatch late every year because I don't want to mess up my show birds by putting them in the breeding pen until March/April. I just hatched my last batch this past weekend. I have never had any trouble with them not achieving their potential size. I think that is a myth or sometimes an excuse for inferior birds. A couple years back I just wanted to see so I hatched some in December and January...then hatched some of the same breed and parents in June. There was no difference in them at maturity. I do fight with Cocci at times but I have had it in January as well so I think that is more of a moisture thing.
Genetics, good food, clean water and space is what determines the potential of your chickens.
Matt
My observation has been similar, mostly. I have not always been breeding, and raising the birds with the mindset I have now. I have been tracking growth rates and size off and on for around 20 years.
Extreme conditions can check their rate of growth, but without additional stressors they tend to ultimately reach a similar size. Eventually. That has been my impression. That is not scientific.
Regardless, when it comes time for selection, I am comparing apples to apples.
I do not believe that every situation is equal. Not everyone manages their birds the same, or has the same environment. I do see it as possible to compound problems to a point where the birds can become stunted.
I have wondered if the quality of feather can be affected in some breeds if periods of stress came at critical points.
I have liked to see my birds reach 65-75% of their adult weight before we would get especially hot. I see it as an ideal. On the other hand, I have not been shy about a later hatch if I chose to. I had July chicks last year, and the average size ended up being similar to the early hatched birds.
My Catalanas are effecting that view. The early hatched birds, molt the first year.
Maybe there is some effect on slow maturing breeds, that do not get to a certain size before the short cod days of winter?
I did wonder what experience that Marcy would have. Her summers are more consistently extreme than ours. I do not think Tucson is quite as bad, but I remember some Phoenix nights that were around 90 at midnight.