The Combination of Dietary Branched-Chain and Limiting Amino Acids Modulates Feed Intake Through Both Peripheral and Central Mechanisms in Pigs Fed with Low Protein Diets

Abstract

Abstract Objectives Due to its negative influence on human health and environment, excess nitrogen excretion is challenging the sustainability of swine industry. Severe reduction of dietary protein may reduce the excretion of nitrogen from swine production, but this results in poor growth performance of pigs. The aim of current study was to investigate the effect of supplementing LP diets with both branched-chain amino acids (BCAA; i.e., leucine, isoleucine, valine) and other limiting amino acids (LAA; i.e., lysine, methionine, threonine, tryptophan) at levels higher than suggested requirements on the growth performance and mRNA and protein abundance of markers associated with feed intake in nursery pigs. Methods Forty-eight weaned barrows at 3 weeks of age were individually housed and following 2 weeks of adaptation, randomly assigned to 6 treatments for 4 weeks: 1) positive control: 20% crude protein (CP); 2) negative control (NC): 14% CP; 3) NC + LAA 25% more than suggested levels (L25); 4) NC + LAA 50% more than suggested levels (L50); 5) NC + LAA and BCAA 25% more than suggested levels (LB25); 6) NC + LAA and BCAA 50% more than suggested levels (LB50). At week 4 of starting experimental diets, all pigs were euthanized and blood samples, hypothalamus and jejunum samples collected. The data were analyzed with univariate GLM (SPSS®). Results Final body weight was significantly higher in LB50 than L50. The pigs fed with LB50 and LB25 had higher average daily feed intake than L50 and L25, respectively. The LB50 reduced the plasma serotonin concentration relative to L50 and NC. The overall effect of diet on mRNA abundance of hypothalamic tryptophan hydroxylase 1 (TPH1) and 5-hydroxytryptamine receptor 2B (5HTR2B) was significant, but no differences among groups were detected. The pigs in LB50 and LB25 had higher mRNA abundance of hypothalamic NPY (∼20%) than NC. Conclusions Supplementing the LP diets with increased levels of both dietary BCAA and LAA reduced the plasma serotonin concentration and improved the growth performance and feed intake partly through increased hypothalamic NPY. Funding Sources This work was supported by Animal Health and Production and Animal Products: Improved Nutritional Performance, Growth, and Lactation of Animals and by Hatch project from the USDA National Institute of Food and Agriculture.