Nitrogen balance of starting barrow pigs fed on increasing lysine levels

the effects of increasing lysine levels on nitrogen balance of pigs fed on low protein diets were evaluated. four treatments (diets) containing lysine levels (0.8, 1.0 1.2 and 1.4%) were applied to 12 starting (20.0 ± 1.8 kg) barrow pigs. methionine, threonine and tryptophan were kept constant to the lysine ratio in all diets. feces and urine were collected during a 5-day period. nitrogen output in urine (nou), total nitrogen output (tno), nitrogen retention (nr), net protein utilization (npu), biological value or feed protein (bvfp), urine urea nitrogen (uun), and plasma urea nitrogen (pun) were determined. pun showed high negative correlations with bvfp (-0.84), npu (-0.76), and nr (-0.78) and a positive correlation (0.79) to nou. lowest nitrogen excretion and the best use of diet protein were obtained with 1.1% total lysine level. pun is efficient to indicate amino acid for pigs.