Nitrogen balance in relation to energy intake in entire male pigs weighing 75 kg.

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 LW0.75 per d) but thereafter remained constant at 22.8 g N/d.