Consumption of a highly fermentable, high energy density (ED) food by ruminants results in changes within the rumen environment including a fall in pH. It has been shown that such changes can influence subsequent intake and diet selection in sheep as they attempt to correct these changes through their feeding behaviour (Cooper et al, 1995). The addition of a buffer eg NaHCO3 to a previously consumed high ED food or offering the sheep a low ED food would assist in preventing changes in the rumen environment hence the ruminant would not need to modify it’s diet selection in an attempt to correct these changes. The objectives were to determine (i) whether or not sheep would make a continuous non random selection between 2 foods of different ED (Test 1), (ii) to determine what concentration of NaHCO3 should be added to a food to obtain the most beneficial effects on rumen pH combined with intake (Test 2), and finally (iii) the main objective was to determine what consequences the ED of a food and the supplementation of NaHCO3 to a food offered for a short period of time had on subsequent diet selection made by sheep (Test 3).