Dietary supplementation with monosodium glutamate is safe and improves growth performance in postweaning pigs.

Dietary intake of glutamate by postweaning pigs is markedly reduced due to low feed consumption. This study was conducted to determine the safety and efficacy of dietary supplementation with monosodium glutamate (MSG) in postweaning pigs. Piglets were weaned at 21 days of age to a corn and soybean meal-based diet supplemented with 0, 0.5, 1, 2, and 4 % MSG (n = 25/group). MSG was added to the basal diet at the expense of cornstarch. At 42 days of age (21 days after weaning), blood samples (10 mL) were obtained from the jugular vein of 25 pigs/group at 1 and 4 h after feeding for hematological and clinical chemistry tests; thereafter, pigs (n = 6/group) were euthanized to obtain tissues for histopathological examinations. Feed intake was not affected by dietary supplementation with 0-2 % MSG and was 15 % lower in pigs supplemented with 4 % MSG compared with the 0 % MSG group. Compared with the control, dietary supplementation with 1, 2 and 4 % MSG dose-dependently increased plasma concentrations of glutamate, glutamine, and other amino acids (including lysine, methionine, phenylalanine and leucine), daily weight gain, and feed efficiency in postweaning pigs. At day 7 postweaning, dietary supplementation with 1-4 % MSG also increased jejunal villus height, DNA content, and antioxidative capacity. The MSG supplementation dose-dependently reduced the incidence of diarrhea during the first week after weaning. All variables in standard hematology and clinical chemistry tests, as well as gross and microscopic structures, did not differ among the five groups of pigs. These results indicate that dietary supplementation with up to 4 % MSG is safe and improves growth performance in postweaning pigs.

Proline and hydroxyproline metabolism: implications for animal and human nutrition.

Proline plays important roles in protein synthesis and structure, metabolism (particularly the synthesis of arginine, polyamines, and glutamate via pyrroline-5-carboxylate), and nutrition, as well as wound healing, antioxidative reactions, and immune responses. On a per-gram basis, proline plus hydroxyproline are most abundant in collagen and milk proteins, and requirements of proline for whole-body protein synthesis are the greatest among all amino acids. Therefore, physiological needs for proline are particularly high during the life cycle. While most mammals (including humans and pigs) can synthesize proline from arginine and glutamine/glutamate, rates of endogenous synthesis are inadequate for neonates, birds, and fish. Thus, work with young pigs (a widely used animal model for studying infant nutrition) has shown that supplementing 0.0, 0.35, 0.7, 1.05, 1.4, and 2.1% proline to a proline-free chemically defined diet containing 0.48% arginine and 2% glutamate dose dependently improved daily growth rate and feed efficiency while reducing concentrations of urea in plasma. Additionally, maximal growth performance of chickens depended on at least 0.8% proline in the diet. Likewise, dietary supplementation with 0.07, 0.14, and 0.28% hydroxyproline (a metabolite of proline) to a plant protein-based diet enhanced weight gains of salmon. Based on its regulatory roles in cellular biochemistry, proline can be considered as a functional amino acid for mammalian, avian, and aquatic species. Further research is warranted to develop effective strategies of dietary supplementation with proline or hydroxyproline to benefit health, growth, and development of animals and humans.

Lactating porcine mammary tissue catabolizes branched-chain amino acids for glutamine and aspartate synthesis.

The uptake of branched-chain amino acids (BCAA) from plasma by lactating porcine mammary gland substantially exceeds their output in milk, whereas glutamine output is 125% greater than its uptake from plasma. In this study, we tested the hypothesis that BCAA are catabolized for glutamine synthesis in mammary tissue. Mammary tissue slices from sows on d 28 of lactation were incubated at 37 degrees C for 1 h in Krebs buffer containing 0.5 or 2 mmol/L l-[1-(14)C]- or l-[U-(14)C]-labeled leucine, isoleucine, or valine. Rates of BCAA transport and degradation in mammary tissue were high, with approximately 60% of transaminated BCAA undergoing oxidative decarboxylation and the remainder being released as branched-chain alpha-ketoacids (BCKA). Most ( approximately 70%) of the decarboxylated BCAA were oxidized to CO(2). Rates of net BCAA transamination were similar to rates of glutamate, glutamine, aspartate, asparagine, and alanine synthesis. Consistent with the metabolic data, mammary tissue expressed BCAA aminotransferase (BCAT), BCKA decarboxylase, glutamine synthetase (GS), glutamate-oxaloacetate aminotransferase, glutamate-pyruvate aminotransferase, and asparagine synthetase, but no phosphate-activated glutaminase, activity. Western blot analysis indicated relatively high levels of mitochondrial and cytosolic isoforms of BCAT, as well as BCKA dehydrogenase and GS proteins in mammary tissue. Our results demonstrate that glutamine and aspartate (abundant amino acids in milk protein) were the major nitrogenous products of BCAA catabolism in lactating porcine mammary tissue and provide a biochemical basis to explain an enrichment of glutamine and aspartate in sow milk.

L-Glutamine or L-alanyl-L-glutamine prevents oxidant- or endotoxin-induced death of neonatal enterocytes.

This study tested the hypothesis that L-glutamine (Gln) or L-alanyl-L-glutamine (Ala-Gln) prevents oxidant- or endotoxin-induced death of neonatal enterocytes. Enterocytes of neonatal pigs rapidly hydrolyzed Ala-Gln and utilized Gln. To determine whether Gln or Ala-Gln has a cytoprotective effect, IPEC-1 cells were cultured for 24 h in Gln-free Dulbecco's modified Eagle's-F12 Ham medium containing 0, 0.5, 2.0 or 5.0 mM Gln or Ala-Gln, and 0, 0.5 mM H(2)O(2) or 30 ng/ml lipopolysaccharide (LPS). Without Gln or Ala-Gln, H(2)O(2)- or LPS-treated cells exhibited almost complete death. Gln or Ala-Gln at 0.5, 2 and 5 mM dose-dependently reduced H(2)O(2)- or LPS-induced cell death by 14, 54 and 95%, respectively, whereas D: -glutamine, alanine, glutamate, ornithine, proline, glucosamine or nucleosides had no effect. To evaluate the effectiveness of Gln or Ala-Gln in vivo, 7-day-old piglets received one-week oral administration of Gln or Ala-Gln (3.42 mmol/kg body weight) twice daily and then a single intraperitoneal injection of LPS (0.1 mg/kg body weight); piglets were euthanized in 24 and 48 h to analyze intestinal apoptotic proteins and morphology. Administration of Gln or Ala-Gln to LPS-challenged piglets increased Gln concentrations in small-intestinal lumen and plasma, reduced intestinal expression of Toll-like receptor-4, active caspase-3 and NFkB, ameliorated intestinal injury, decreased rectal temperature, and enhanced growth performance. These results demonstrate a protective effect of Gln or Ala-Gln against H(2)O(2)- or LPS-induced enterocyte death. The findings support addition of Gln or Ala-Gln to current Gln-free pediatric amino acid solutions to prevent intestinal oxidative injury and inflammatory disease in neonates.

Arginine nutrition in neonatal pigs.

The concentration of arginine (an essential amino acid for neonates) in sow's milk is remarkably low, and thus endogenous synthesis of arginine plays a crucial role in maintaining arginine homeostasis in milk-fed piglets. Paradoxically, intestinal synthesis of citrulline from glutamine/glutamate and proline (the endogenous source of arginine) declines markedly in 7- to 21-d-old suckling pigs, compared with 1- to 3-d-old pigs. Therefore, plasma concentrations of arginine and its immediate precursors (ornithine and citrulline) decrease progressively by 20-41%, whereas plasma ammonia levels increase progressively by 18-46%, between d 3 and 14 of life. Dietary supplementation of 0.2 and 0.4% arginine to 7- to 21-d-old pigs (artificially reared on a milk feeding system) dose dependently enhances the plasma arginine concentration (30 and 61%), reduces the plasma ammonia level (20 and 35%), and increases weight gain (28 and 66%). These compelling metabolic and growth data demonstrate unequivocally that arginine is insufficient for supporting the maximal growth in milk-fed young pigs and that this arginine deficiency represents a major obstacle to realizing the growth potential in piglets. A low concentration of mitochondrial N-acetylglutamate (an activator of both pyrroline-5-carboxylate synthase and carbamoylphosphate synthase-I) is responsible for the striking decline in the intestinal synthesis of citrulline and arginine during the suckling period. Accordingly, oral administration of N-carbamoylglutamate [a metabolically stable analogue of N-acetylglutamate; 2 x 50 mg/(kg body wt . d)] enhances plasma arginine level (68%) and weight gain (61%) of 4- to 14-d-old sow-reared pigs. Thus, the metabolic activation of intestinal citrulline and arginine synthesis provides a novel, effective means to increase endogenous arginine provision and therefore piglet growth (a major goal of animal agriculture). Our findings not only generate new fundamental knowledge about amino acid utilization by neonatal pigs, but they also have important practical implications for improving the efficiency of pork production.