Whilst our previous work (Hou et al, 1991) has shown that sheep will make structured selections amongst pairs of feeds offered as a choice, we have not been able to relate these selections to the animals requirements as estimated by relative performance as single feeds. Also the nature of crude protein in diets offered as a choice has not been used as a variable.

The objective of the experiment was to develop the proposition that growing sheep, when given a choice between a suitable pair of foods, will select a diet that meets their protein requirements by using pairs of foods to be given as a choice and also offering each food singly to sheep, in order to quantify the effects of the foods on performance. In order to address an aspect of the extent to which sheep may make selections between diets to satisfy digestive (rumen) function rather than metabolic needs we have also included urea supplementation of an otherwise low CP diet amongst the foods offered as a choice.