Threonine requirement of neonatal piglets receiving total parenteral nutrition is considerably lower than that of piglets receiving an identical diet intragastrically.

Evidence is accumulating that the amino acid requirements for neonates receiving total parenteral nutrition (TPN) are significantly different than those for oral feeding and need to be determined. The parenteral threonine requirement was determined in 3-d-old male Yorkshire piglets (n = 25) by examining the effect of varying dietary threonine intakes [0.05-0.6 g/(kg.d)] on phenylalanine oxidation. The diet included adequate energy, total amino acids and phenylalanine, with excess tyrosine. Phenylalanine kinetics were determined from a primed, continuous intravenous infusion of L-[1-14C]phenylalanine. Phenylalanine oxidation, estimated from the rate of 14CO2 released in expired air during isotope infusion, decreased (P < 0.05) as threonine intake increased from 0.05 to 0.15 g/(kg.d) and was low and constant for threonine intakes >0.15 g/(kg.d). Using breakpoint analysis with 95% confidence interval (CI), mean requirement and safe level of parenteral threonine intake were estimated to be 0.19 and 0.21 g/(kg. d), respectively (equivalent to 13 and 14 mg/g amino acids, respectively). To compare these data with those of orally fed controls, we then repeated the experiment by infusing identical diets intragastrically to piglets (n = 25); the varying dietary threonine intakes were 0.1-1.2 g/(kg.d). Employing identical kinetics and analyses, the mean requirement and safe level of oral threonine intake were estimated to be 0.42 and 0.51 g/(kg.d), respectively (equivalent to 28 and 34 mg/g amino acids, respectively). These data demonstrate that the threonine requirement of neonates during TPN is approximately 45% of the mean oral requirement.