Not only were the Heritage breeds much larger, but they had more muscle (MEAT, folks) on their bones from never having been confined in tiny coops (see chicken tractors here). Most times these were hatched by a broodie, and had the run of the yard after 2 weeks old. They developed muscle mass in legs , wings, and breast (pectoral muscles, ladies) While running and flying about the yard.
Compared to what we buy now from a hatchery, the heritage breeds were much larger. I remember a time when hatcheries sold chicks that were more true to type; you could easily separate the chickens if you had ordered RIRs, NHs, and mixed in some of the 'new' production reds to boot. Leghorn cockerels did make great fryers; they were larger than today's laying strains, laid less eggs in that first year, but were productive layers for about three years. Though breeding and maintaining of pure, heritage chickens [as well as every breed of livestock] was starting to change even before my early childhood, some still kept the heritage breeds strictly for their original utility value, and the breeds chosen by which ones best met their needs or preferences. In fact, someone breeding with a lot of emphasis on producing a show winner would have been looked down on by some folks as "ruining" the breed, and a show strain and a heritage strain were two different lines. [There was no chance that a heritage breeder was going to use a Leghorn hen to breed with if she was a mediocre layer, just because won every show she was entered in.]
Not knockin' on show breeders, the heritage breeds are still in existence [for the most part] only because of them, and I hope to show my birds [large fowl Cornish] someday.
This is something I encourage my Buff Orps to do today. What a difference it had made !
