What exactly is a Jumbo Cornish Cross a cross of?
None of the "Cornish cross" birds, jumbo or otherwise, are first crosses. They're commercial hybrids developed for the meat market & bred from highly specialised lines. Presumably with Indian game (Cornish game) & Plymouth Rock somehwere in...
Traditionally the Indian Game (called Cornish Game in US) was used as a farmyard cross to Dorkings, Sussex & other dual purpose breeds etc. to produce good table birds. Indian game do not grow particularly fast so there is no problem there & they give a fair sized carcass. Indian game hens make...