Darn this sort of thing raises my hackles!
MSM is metely mechanically separated meat. The reason spent hen is mechanically de-boned is because the carcuss is very slim with little meat. This is jsut because of the bird's genetics, nothing more. In other words, this breed tends to be a good deal lighter in muscle. But Granny made all her soup from spent hen, because it had a bunch more flavour. And, while it is not a roaster, it is a "fricasee chicken" which means it is both old and tough, unless one cooks it for a long time. This is a result of old ligamentous and conne4ctive tissue, wghich is very tough. But cut it fine enough for sausage and there is no problem. In fact it superior, more intense flavour is a big plus. Its all about marketing and the big guys are happy to eliminate at elast one competitor at any time.