Single Comb White Leghorn hens of 2 ages (44 and 80 weeks) were fed diets of different energy (10.88, 12.13 or 13.39 MJ ME and 140 g protein/kg) or protein (120, 140, 160 or 180 g and 12.13 MJ ME/kg) concentration over an 8-week period. 2. Food intake did not change with increasing concentrations of dietary protein. Protein intake was directly correlated with dietary protein concentration. 3. Energy intake increased with dietary energy concentration but, generally, failed to match the increases in dietary energy concentration. Energy, rather than protein, concentration was the major determinant of food intake. 4. Efficiency of energy utilisation decreased and mean adipocyte size increased with higher energy intake. 5. A bimodal adipocyte size distribution, consisting of a primary large size and a secondary small size population, was present in the abdominal fat pad of birds of both ages. There was no significant difference in the numbers of large adipocytes between the hens of the two ages. 6. The greater mean fat pad weight in the older hens was associated with increased mean cell volume in the population of large adipocytes.
