As genetic selection within the dairy herd establishes milking machines with higher yields and apparently greater efficiency, their ability to consume additional feed has not kept pace with their ability to produce milk. This poses an increasing challenge to farmers and their advisors.

Spring and the introduction of grazing further complicates the above problem since it is difficult to control and accurately predict the quantity of grass consumed. Variations in feed intake, particularly if inadequate concentrates or buffer feeds are available, could present a serious challenge resulting in depressed milk yield and quality, increased mobilisation of body reserves and impaired fertility.