Digestion, assimilation and metabolism of lean and fatty pork were studied in immature C. porosus. 2. Up to 92% of protein was digested but protein digestion was adversely affected by high levels of dietary fat. 3. Protein was catabolized in preference to fat, much of which was stored, although the ratio between metabolizable energy and protein retention was still 2.73 g/100 kJ. 4. 56.8% of ingested energy was stored, maintenance requirements taking as little as 7.7%. 5. Up to 13.8% energy was spent digesting and assimilating food.