Yearling heifers at grass in early spring on the demonstration farm.\ Philip Doyle While measuring the physical performance of animals is important and gives farmers a good indication that production targets are being constantly met, these systems need to stack up financially if they are to have a sustainable future on Irish farms. Diet proportions Figures 1 and 2 show the makeup of each proportion of the diet on a dry matter (DM) basis for heifers and steers. This shows that grazed grass is making up two-thirds of the heifers’ lifetime diet on farm while the bullocks are just slightly behind this at 62%.