Apart from the kale crop, there is no information on the amounts of nutrients absorbed from lambs ingesting forage brassica crops. In particular, knowledge of the amounts of OM apparently digested in the rumen and of the non-ammonia N (NAN) flows at the abomasum are important in predicting the amount of nutrients absorbed and consequently carcase gains. One experiment was conducted using the leaf components of rape and hybrid turnip to describe nutrient supply and to identify whether carcase gains would be limited by the supply of energy substrates or protein to the tissues. A second experiment was conducted with lambs grazing the leaf of both crops and given supplements to test the hypothesis that carcase gains were limited by the supply of energy substrates.