This is a classic Cornish Rock. They're the standard broiler chicken that you buy in the grocery store in a Styrofoam tray wrapped in plastic. They eat a ridiculous amount of food, produce a ridiculous amount of waste, and grow ridiculously fast. These birds can go from day old to slaughter in as little as six weeks.
In general, when they arrive at the abattoir they look like hell. They're dirty, only partially feathered, and can often barely walk.
If you take care of them, though, controlling their feed intake and making sure that their accommodations are clean, you can actually produce a decent looking Cornish Rock.
I'm always amused when the first line inspector comes and asks to take a look and says, "Those are nice looking birds." Thanks.
This year we ordered our spring chicks early and our abattoir decided to start processing two weeks later than usual. That meant that our Cornish Rocks were finished two weeks before we could have them processed. We picked out the largest birds and processed them ourselves then cut back on their feed, made sure they had LOTS of clean water, and cleaned their bedding every two days.
The birds our abattoir processed finished, in the bag, with no water in the cavity (like you get at the grocery store) averaging 3.5 Kg (8 lb) and topping out at 4.5 Kg (10 lb). That's getting up into turkey range.
When we raised them (60 birds) we found the meat too chewy. It was one of the factors in not continuing.
The meat is different, for sure. Most people are used to injected grocery store chickens. Letting them sit in the fridge for a day or two after they are processed really helps.