Dietary supplementation with excess leucine transiently improved whole body nitrogen retention in young pigs challenged with bacterial lipopolysaccharide
The increase in circulating pro-inflammatory cytokines following a bacterial lipopolysaccharide (LPS) challenge causes a disruption in normal nitrogen (N) and amino acid (AA) metabolism. The reduction in whole body N retention during inflammation can be attributed to an increase in hepatic protein synthesis at the expense of muscle protein synthesis, which may be modulated by leucine (Leu) intake. The objective of this study was to explore the effect of excess dietary Leu on the dynamics of N retention in young pigs following an LPS challenge. A total of 24 starter pigs (13.93 ± 2.05 kg) were used in a 2×2 factorial design (n = 6). Pigs were fed isoenergetic and isonitrogenous diets formulated to contain all essential AA 10% above requirements for protein deposition (Con; 1.36% SID Leu) or Leu supplemented at twice that amount (+Leu; 2.72% SID Leu). Pigs were housed in metabolic crates and fed six times daily according to their body weight. Pigs were challenged with either saline (-LPS) or repeated and increasing doses of LPS (+LPS; 30 µg·kg-1 injected intramuscularly on days 1, 3, 5, and 7 of a 7-d N-balance period). Blood was collected on days 1 and 7 one hour after feeding to determine plasma AA concentrations. Whole body N retention was determined daily. Pigs fed +Leu had higher plasma Leu than pigs fed Con (319 vs 159 µmol·L-1, SE 10.3, P < 0.01). There was no effect of diet on N retention across the 7-d N balance period (P > 0.10). However, LPS reduced N retention during the first 3 days of the N balance period (P < 0.05). For +LPS pigs, the effect of diet on N retention changed over time (P < 0.05); on day 2, N retention was lower in +LPS pigs fed Con than +LPS pigs fed +Leu (10.5 vs 12.3 g/d, SE 0.66, P < 0.05). Moreover, N retention was higher in -LPS pigs than in +LPS pigs fed Con (13.0 vs 10.5 g/d, SE 0.66, P < 0.01) whereas N retention was not different between –LPS pigs and +LPS pigs fed +Leu (12.3 vs 12.3 g/d, SE 0.66, P > 0.10) on day 2 post-challenge. In this study, excess dietary Leu partly attenuated the reduction in body protein gain after an LPS challenge.
endotoxin, leucine, nitrogen retention