The Belgian Blue... While it’s a natural occurrence, some still claim the animal’s muscle mass is because of steroid injections due to the large muscle development. The Belgian Blue is however not born with that extreme muscle, but starts developing it at 4 to 6 weeks old. Belgian Blue beef outclasses all other beef breeds in carcass yield (up to 80%). When used in crossbreeding programmes with other dairy or beef breeds, it increases carcass yield from 5 to 7 % compared to the maternal line.