This project was designed to determine the ideal forage:concentrate ratio for market lambs by looking at indicators of growth performance and rumen health. Forty-three Rideau-Arcott/Dorset ram lambs (~30 kg) were randomly assigned to one of six dietary treatments (100%, 80%, 60%, 40%, 20%, and 0% chopped hay, with the remainder of the diet concentrate [primarily ground corn (64.7% DM basis) and DDGS (31.8% DM basis)]. Continuous reticular-rumen pH measurements were recorded from d1 to d14 and from d35 to d49. At slaughter, rumen health and liver abscess scores were recorded for each lamb. Results included time spent in sub-acute and acute acidosis, papillae morphology, average daily gain, average daily intake, feed:gain ratio, and final weights across diets. Understanding how dietary fibre requirements impact rumen pH can result in more cost-efficient diets, while maintaining animal health and growth performance.