Previous studies of diet selection, in a controlled environment (Hou et al, 1991; Kyriazakis & Oldham, 1992) have demonstrated that growing lambs are able to select, from foods differing in crude protein content, a diet which meets their requirements for protein. Little consideration has been given to the effect of other physiological states upon diet selection. The ewe in the last eight weeks before lambing has been chosen as further model; during this period ewes have an increasing requirement for metabolisable energy and protein in order to supply the growth and development of the foetus and maternal tissues. In addition the foetus has an increasing absolute requirement for glucose, which must be supplied by the ewe herself via gluconeogenesis.

The objective of this experiment was determine whether ewes are able to select a diet, from a pair of foods, which enables them to supply these requirements for metabolisable energy and protein. Secondly it was hoped that the size of the pool of non amino precursors could be altered and so it would be possible to test whether the availability of such precursors would have an influence upon the selection for protein.