An operant conditioning technique was used to determine whether the reinforcement value of grains and seeds preferred by sheep could be increased by crushing the food. Five sheep were trained to press a plate to receive a food reward. The rate of pressing on a progressive fixed ratio schedule of reinforcement was used as a measure of reinforcement value. Five foods were tested: barley, wheat, oats, lupins and peas. Crushing the foods had no effect on rate of pressing, whereas there was a great deal of variation between sheep and between foods. The preferred foods were wheat and barley.