Incorporation of nitrogen-15 from dietary [15N] diammonium citrate into amino acids of liver and muscle proteins in germfree and specific-pathogen-free neonatal pigs.

Incorporation of 15N from dietary [15N]diammonium citrate ([15N]DAC) into amino acids isolated from hydrolyzed tissue proteins was investigated in the presence or absence of intestinal flora in neonatal pigs. The 15N was incorporated into all of the essential and nonessential amino acids from liver and muscles in one of two germfree pigs and two specific-pathogen-free pigs which were killed on the 5th day after the administration of [15N]DAC. But, a higher 15N concentration than natural abundance of 15N was not detected in histidine, lysine, and threonine from these tissues in another germfree pig killed the next day. Nitrogen transfer from DAC into all amino acids, including these three essential amino acids, may be possible in the specific-pathogen-free pig and even in the germfree pig.