Lysine, threonine and tryptophan postprandial metabolism in LPS challenged growing pigs

Abstract

Sanitary challenges and/or immune system activation are associated with decreased voluntary feed intake,increased metabolic rate and energy expenditure, and alterations on nutrient utilization in growing pigs.As a consequence, animals weight gain and feed efficiency are negatively impacted in such conditions.The aim of this study was then to evaluate the effects of an inflammatory challenge caused by repeatedinjections of Escherichia coli lipopolysaccharide (LPS) on lysine, threonine and tryptophan postprandialmetabolism. Fourteen growing pigs fitted with a jugular catheter were housed in a temperature-controlledroom in which ambient temperature was maintained constant at 24°C. The experimental period lasted 17 daysthat was subdivided in a seven days period before and a 10 days period during the inflammatory challengethat consisted in five repeated injections of LPS at two days intervals. The initial dose of 30 μg/kg of bodyweight was increased by 12% at each subsequent injection to circumvent adaptive endotoxin resistance tothe repeated inflammatory stimuli. Before the LPS- challenge (baseline), and 24h after the second (T1) andthe fourth (T2) LPS injections, 300 g of feed was given to pigs previously fasted overnight and serial bloodsamples were taken over four-hours to measure plasma amino acids concentrations. Amino acids postprandialconcentrations were analyzed using the linear MIXED procedure of SAS including the fixed effects of timepoints (baseline, T1 or T2). Relative to baseline, postprandial concentrations of lysine were lower at T1and greater at T2. In addition, the LPS-challenge induced a long-lasting (at T1 and T2) reduction in plasmapostprandial concentrations of threonine and tryptophan. Firstly, these results suggest a short-term increasedutilization of lysine to be used as energy source during the LPS-challenge. Then, lysine demand decreasesin association with a lower protein synthesis for growth. Secondly, they evidence an increased threonineand tryptophan metabolic demand to support the requirements of the immune response. For instance, theimmune system activation induces the synthesis of acute phase proteins that, in turn, have greater amounts ofthreonine and tryptophan in their compositions. Finally, our evidences that an inflammatory challenge causedby LPS leads to significant changes on amino acids metabolism and partitioning. induces significant changesin the postprandial metabolism of growing pigs. These findings may contribute to redefine pigs nutritionalrequirements during inflammatory and/or immune challenges