July 14, 2019

Interpretive Summary: Immune Stimulation and its effects on plasma acid levels in growing pigs

Interpretive Summary: Immune system stimulation induced by Escherichia coli lipopolysaccharide alters plasma free amino acid flux and dietary nitrogen utilization in growing pigs

By: Dr. Caitlin Vonderohe

Immune system stimulation affects the use of amino acids, which subsequently negatively affects growth performance in growing pigs by redistributing amino acids away from muscle deposition, and toward the immune system. When the immune system is stimulated, proteins such as acute phase proteins, immunoglobulins are synthesized, increasing the requirements for specific amino acids. Previous research exploring how immune stimulation affects specific amino acid metabolism has been largely inconsistent. This inconsistency may be due to investigators using different models of immune stimulation, differences in nutritional approach, and different amino acid measurement techniques. A recent study published in the Journal of Animal Science, entitled “Immune system stimulation induced by Escherichia coli lipopolysaccharide alters plasma free amino acid flux and dietary nitrogen utilization in growing pigs” explored how immune stimulation affects the plasma amino acid levels and flux.

Investigators surgically placed jugular catheters in ten gilts. These gilts were housed in metabolism crates and fed a corn and soybean meal-based diet. After 6 days of recovery from surgery, gilts underwent a nitrogen balance study prior to immune system stimulation. Immune stimulation was achieved by repeated injections of E. coli lipopolysaccharide in half of the gilts. The rest of the gilts received repeated injections of sterile saline. Isotope-labeled amino acids were infused through the jugular catheter. Nitrogen balance was measured by analysis of urine, feces and feed. Blood samples were taken before and after infusion of isotope-labeled amino acids in to the jugular catheters. Blood chemistry and hematology were used to assess the efficacy of LPS as an immune stimulant. After the conclusion of the isotope tracer study, pigs were euthanized and ileal digesta was collected for analysis for N content to measure apparent ileal digestibility.

LPS infusion caused a reduction in daily feed intake, greater degree of lethargy and fever. Most hemotologic and blood chemistry measurement were similar between immune stimulated- and control gilts. However, immune-stimulated pigs had a greater anion-gap which is a measure of acid-base balance. Immune stimulation did not affect N intake and total excretion but tended to reduce N retention. Apparent ileal digestibility was decreased by 17.3% in immune stimulated pigs compared to control animals. Immune stimulation decreased plasma flux of Isoleucine and Phenylalanine and tended to decrease plasma flux of Lysine.

Overall, the investigators successfully induced a systemic inflammatory immune response and found changes in nitrogen retention, apparent ileal digestibility, and amino acid flux after immune stimulation. Immune-stimulated pigs tended to retain less protein, and there were differences in plasma flux of Isoleucine and Phenylalanine. This result indicates that immune stimulation reduces the requirement for branch-chain amino acids and phenylalanine. There was also a tendency for immune stimulation to decrease lysine flux, which may reflect systemically reduced protein synthesis.