Nitrogen Absorbed from the Large Intestine Increases Whole-Body Nitrogen Retention in Pigs Fed a Diet Deficient in Dispensable Amino Acid Nitrogen1–3

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Background: Nitrogen absorption from the large intestine is considered of limited value for supporting body protein synthesis in animals and humans, but it may be of benefit when the dietary supply of nitrogen for synthesis of dispensable amino acids (DAAs) is deficient.Objective: A whole-body nitrogen balance study was conducted to evaluate the impact of nitrogen absorption from the large intestine of pigs fed a diet deficient in DAA nitrogen.Methods: Nine cecally cannulated barrows were fed a cornstarch and casein-based diet with a high indispensable amino acid (IAA) nitrogen to total nitrogen ratio (IAA:TN; 0.75). Pigs were randomly assigned to saline or 1 of 2 urea nitrogen infusion rates into the cecum (low and high, 1.5 and 3.0 g/d, respectively) following a 3 × 3 Latin square design. At the high urea nitrogen infusion rate, IAA:TN was 0.55. At slaughter, liver samples were taken to measure activity of carbamoyl phosphate synthetase I (CPS-I), glutamate dehydrogenase (GDH), and Gln synthetase (Gln-S).Results: Whole-body nitrogen retention improved with urea infusion (4.86 ± 0.20 g/d, 6.40 ± 0.21 g/d, and 7.75 ± 0.19 g/d for saline and low and high infusion rates, respectively; P < 0.05), as well as body weight gain. The marginal efficiency of using nitrogen absorbed from the large intestine for improving nitrogen retention was not affected by urea nitrogen infusion rate (P > 0.10). Enzyme activity of CPS-I or Gln-S was not different between treatments (P > 0.10), but GDH showed a trend for a positive linear response with increasing urea nitrogen infusion rate (P = 0.06).Conclusion: These results indicate that urea nitrogen absorbed from the large intestine is efficiently used for increasing body protein deposition when feeding pigs a diet deficient in DAA nitrogen.