Use of by-products and supplementary protein in dairy cow nutrition

The new systems of protein evaluation distinguish clearly between the requirement of the rumen microbes and the need of the host animal. While the requirement of the rumen microbes and the production of microbial protein is related to fermented energy, the need of the host animal varies with type and level of productivity. In dairy cows microbial protein is insufficient for the host animal, particularly when the animals are in negative energy balance, and in order to efficiently utilise body energy reserves undegraded protein must be given. Several experiments are discussed in which dairy cows have been given ammonia treated straw as the only source of roughage and where milk yields have been maintained. It is emphasised that increased use of high roughage diets in early lactation increases the demand for undegraded proteins. The converse is also true: that undegraded protein increases the proportion of roughage that can be used for high yielding dairy cows.