1. Nitrogen balance (NB) was determined in entire male pigs weighing 75.6 (SE 0.56) kg and given 1.43 MJ metabolizable energy (ME)/kg live weight (LW)0.75 per d of semi-synthetic liquid diets which varied in crude protein (N x 6.38):ME from 2.5 to 14.5 g/MJ. Maximum NB of 20.8 g/d was reached with diets containing at least 6.2 g protein/MJ ME.
2. The relation between energy intake and NB was then examined in pigs of comparable live weight (mean 73.8 (SE 0.39) kg) and receiving a liquid diet not limiting in protein. The diet, containing 10.0 g protein/MJ ME, was given at eight rates from 0.24 MJ ME/kg LW0.75 per d to ad lib. by approximately equal increments. Two animals were allocated to each level and two animals were fasted during the balance period.
3. The animals fed ad lib. achieved a mean intake of 1.84 MJ ME/kg LW0.75 per d. NB increased linearly as ME intake increased up to 27.6 MJ/d (1.096 MJ/kg LW0.75per d) but thereafter remained constant at 22.8 g N/d.