Hello from Australia, just to put you straight the use of sake mash is most probably due to convenience, there are A few feedlots over here who specialise in long feeding wagyu for the Japanese market & to my knowledge none use any grain byproducts. They are all very secretive about their ration . The ration changes as the animal develops & the marbling attributes of the wagyu are harnessed,.the feeding can take up to 600 days usually 400-500 , The ration I have seen fed to the wagyu cattle I sold to a feeder is very high in fibre & low in grain to get A gradual weight gain without laying on external fat,about .8kg/day is normal.The meat is A whole new ballgame though & is unique in flavour albeit A bit expensive. All the best
regards
Tully
Australia