Four diets containing 9·6 MJ metabolizable energy (ME) per kg dry matter (DM) (LMEC), and four diets containing 11·3 MJ/kg DM (HMEC) were formulated. One diet of each ME concentration contained 90 g crude protein (CP) per kg DM and served as a negative control (NC). In the three other diets of each ME concentration, the level of CP was raised to 140 g/kg DM by inclusion of poultry litter (PL), non-protein nitrogen (NPN) or fish meal (FM). These diets were examined in a digestion and N balance trial and in a feeding trial.
For the NC, PL, NPN and FM subtreatments of the LMEC diets, DM intakes were 107·1, 112·4, 100·6 and 130·2 g/kg M075 respectively; digestibility coefficients of organic matter (OM) were 0·64, 0·70, 0·67 and 0·71 respectively; and N retention 0·40, 0·76, 0·53 and 1·21 g/kg M075 respectively. For the respective subtreatments of the HMEC diets, the values were: 100·4, 119·4, 109·3, 107·5 for DM intake; 0·64, 0·73, 0·73, 0·73 for digestibility coefficients of OM and 0·40, 0·87, 1·06 and 1·03 g/kg M075 for N retention.
Daily gain on the respective diets in the first 130 days of the feeding trial was 0·85, 0·90, 0·91, 1·04 kg for the LMEC and 1·09, 1·21, 119, 1·24 kg for the HMEC diets, and from the 131st day to slaughter was 0·98, 1·02, 100, 1·08 kg for the LMEC and 1·03, 1·02, 1·07, 1·05 kg for the HMEC diets respectively. Daily carcass gain was 0·49, 0·51, 0·51, 0·53 kg for the LMEC and 0·55, 0·59, 0·59, 0·60 kg for the HMEC diets, respectively.
The relationship between ME concentration in the diet and source of CP is discussed.