Determining the role of tryptophan, isoleucine and valine in regulation of growth and nutrient metabolism in young pigs

Abstract

Tryptophan (Trp), Isoleucine (Ile) and valine (Val) play important roles on variety of physiological processes, but their mechanisms of action on regulation of growth and nutrients metabolism are not fully understood. The objective of study 1 was to assess the effect of dietary Trp on glucose and fat metabolism in a low birthweight piglet model. Seven-day-old piglets were assigned to 4 treatments: normal birthweight-0%Trp, Low Birth Weight-0%Trp (LBW-T0), LBW-0.4%Trp, and LBW-0.8%Trp for 3 weeks. The results of study 1 showed that Trp improved the hepatic lipid and glucose metabolism by reducing the lipogenesis, gluconeogenesis, and glucose efflux and increasing the lipolysis and glycolysis in LBW piglets. The objective of study 2 was to investigate the effect of a mixture of Val above and Ile at NRC levels on growth, nutrient digestibility and gut microbiota in pigs fed with very low protein (VLP) diets. Forty, three-week-old weaned piglets were randomly assigned to following dietary groups (8 pigs/group) for 5 weeks: positive control (PC): normal protein diet; negative control (NC): VLP diet with first four limiting amino acids (FFL, i.e., Lys, Met, Thr, and Trp) at NRC levels; VA: NC with Val above NRC; IL: NC with Ile at NRC level; VAIL: NC with Val above and Ile at NRC levels. In this study we showed that VAIL partially improved the growth performance which is likely linked with alterations in gut microbiota composition. The objective of study 3 was to investigate the effect of dietary Val and Ile on gene and protein expression of key rate limiting enzymes of urea cycle and lipid metabolism in pigs fed with VLP diets. Forty, three-week-old, weaned barrows were assigned to 5 treatments: 1) PC: normal protein diet; 2) NC: VLP diet containing FFL at NRC levels; 3) HV: NC with Val above NRC; 4) HI: NC with Ile above NRC; 5) HVI: NC with both Val and Ile above NRC. The results of study 3 demonstrated that a combination of dietary Val and Ile improved the growth, feed intake, and glucose clearance and decreased the rate of lipogenesis induced by VLP diets.