This fine specimen, known as the Belgian Blue, has experienced "double muscling" due to a gene that suppresses the production of myostatin, a protein that normally inhibits muscle growth after a certain point of development.
Scientists have already inhibited the myostatin gene in mice and are working on blocking the gene in humans in order to treat muscle wasting diseases such as muscular dystrophy. A pharmaceutical company called Acceleron is developing a myostatin inhibiting drug called ACE-031 that will mimic this effect in humans.
source: http://www.sentientdevelopments.com/2009/02/enter-supercow.html
