The experimental diet (Table 1) was formulated to contain 50% crude protein, 20% lipid and 19 MJ/kg digestible energy (DE) on an as-fed basis with a digestible protein (DP) to DE ratio of 23 g DP/MJ DE (assuming a protein digestibility of 90%). Dry ingredients were finely ground (< 800 μm) using a laboratory hammer mill (model 3100, Perten