Dietary L-homoserine spares threonine in chicks.

Four chick bioassays were conducted to evaluate the threonine (Thr) replacement value of l-homoserine (HS). Growth rate was increased (P < 0.05) by dietary addition of 800 mg l-HS/kg diet to a purified diet severely deficient in Thr or by the addition of 800 or 1000 mg of l-HS/kg diet to a corn-peanut meal diet distinctly deficient in Thr.

Advances in protein-amino acid nutrition of poultry.

The ideal protein concept has allowed progress in defining requirements as well as the limiting order of amino acids in corn, soybean meal, and a corn-soybean meal mixture for growth of young chicks. Recent evidence suggests that glycine (or serine) is a key limiting amino acid in reduced protein [23% crude protein (CP) reduced to 16% CP] corn-soybean meal diets for broiler chicks. Research with sulfur amino acids has revealed that small excesses of cysteine are growth depressing in chicks fed methionine-deficient diets.

Excess dietary L-cysteine causes lethal metabolic acidosis in chicks.

A 72-h time-course study was conducted to elucidate the physiological mechanism underlying cysteine (Cys) toxicity in chicks beginning at 8-d posthatch. Biochemical markers quantified in plasma and liver samples collected from chicks receiving 30 g/kg excess dietary Cys were compared with baseline measurements from chicks receiving an unsupplemented corn-soybean meal diet over a 72-h feeding period. Concomitant with chick mortality were indices of acute metabolic acidosis, including a rapid increase (P < 0.

Animal models in nutrition research.

Current knowledge in nutrition is based largely on the use of appropriate animal models together with defined diets. Numerous examples are cited where animal models have been used to solve nutrient x nutrient interactions, to evaluate bioavailability of nutrients and nutrient precursors, and to test for nutrient tolerances and toxicities. Advantages, disadvantages, and idiosyncrasies of various animal species are discussed.

Betaine can partially spare choline in chicks but only when added to diets containing a minimal level of choline.

The ability of betaine to serve as a methyl donor in chicks was assessed in 3 bioassays using a choline-free purified diet that contained adequate methionine (Met). In assay 1, choline and betaine were each supplemented at 300 mg/kg in a 2 x 2 factorial arrangement of diets. Supplemental choline improved (P < 0.

2-keto-4-(methylthio)butyric acid (keto analog of methionine) is a safe and efficacious precursor of L-methionine in chicks.

Relative bioefficacy and toxicity of Met precursor compounds were investigated in young chicks. The effectiveness of DL-Met and 2-keto-4-(methylthio)butyric acid (Keto-Met) to serve as L-Met precursors was quantified using Met-deficient diets of differing composition. Efficacy was based on slope-ratio and standard-curve methodology.

Lysine, arginine, and related amino acids: an introduction to the 6th amino acid assessment workshop.

The focus of the 6th workshop is on lysine, arginine, and related amino acids. Functions, metabolic pathways, clinical uses, and upper tolerance intakes are emphasized in the articles that follow. Lysine is arguably the most deficient amino acid in the food supply of countries where poverty exists, and since the discovery of the nitric oxide synthase pathway, arginine has come into prominence clinically because of the role of nitric oxide in cardiovascular physiology and pathophysiology.

Excess dietary L-cysteine, but not L-cystine, is lethal for chicks but not for rats or pigs.

A comparative species investigation of the relative pharmacologic effects of sulfur amino acids was conducted using young chicks, rats, and pigs. Ingestion of excess Met, Cys, or Cys-Cys supplemented at 2.5-, 5.

Comparative species utilization and toxicity of sulfur amino acids.

Animal studies have shown that several methionine (Met) and cysteine (Cys) analogs or precursors have L-Met- and L-Cys-sparing activity. Relative oral bioavailability (RBV) values, with the L-isomer of Met and Cys set at 100% (isosulfurous basis), are near 100% for D-Met for animals but only about 30% for humans. Both the OH and keto analogs of Met have high RBV-sparing values, as does N-acetyl-L-Met (the D-isomer of acetylated Met has no bioactivity).

Comparative nutrition and metabolism: explication of open questions with emphasis on protein and amino acids.

The 20th century saw numerous important discoveries in the nutritional sciences. Nonetheless, many unresolved questions still remain. Fifteen questions dealing with amino acid nutrition and metabolism are posed in this review.

Dietary S-methylmethionine, a component of foods, has choline-sparing activity in chickens.

Acid hydrolysis of dehulled soybean meal (SBM) and corn gluten meal (CGM) followed by chromatographic amino acid analysis (ninhydrin detection) revealed substantial quantities of S-methylmethionine (SMM) in both ingredients (1.65 g SMM/kg SBM; 0.5 g SMM/kg CGM).

Tolerance for branched-chain amino acids in experimental animals and humans.

There is no good evidence for establishing branched-chain amino acid (BCAA) tolerance levels for humans. With pigs, chicks, and rats, data are available concerning excessive intake levels of BCAA, but most of the information is for growing animals instead of for adults. Estimates of maintenance requirements for (high-quality) protein and BCAA in pigs weighing between 43 and 140 kg are 350 mg .

Decreased protein accretion in pigs with viral and bacterial pneumonia is associated with increased myostatin expression in muscle.

Chronic respiratory infections reduce growth in pigs but protein accretion (PA) during an ongoing multifactorial respiratory infection has not been determined, and the mechanisms underlying growth inhibition are largely unknown. The objectives of this study were to determine whether viral and bacterial pneumonia in young pigs decrease PA, increase serum IL-1beta and IL-6, and increase myostatin (MSTN) mRNA in biceps femoris and triceps muscles. Mycoplasma hyopneumoniae (Mh) or medium was given intratracheally at 4 wk of age, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) or medium was given intranasally at 6 wk of age, and pigs were killed 7 or 14 d after PRRSV inoculation for body composition analysis.

Supplementation of total parenteral nutrition with butyrate acutely increases structural aspects of intestinal adaptation after an 80% jejunoileal resection in neonatal piglets.

Background: Supplementation of total parenteral nutrition (TPN) with a mixture of short-chain fatty acids (SCFA) enhances intestinal adaptation in the adult rodent model. However, the ability and timing of SCFA to augment adaptation in the neonatal intestine is unknown. Furthermore, the specific SCFA inducing the intestinotrophic effects and underlying regulatory mechanism(s) are unclear.

Animal models of human amino acid responses.

The principal differences between experimental animals and humans with regard to amino acid responses are 1) growing animals partition most of their amino acid intake to protein accretion, whereas growing children partition most of their intake to maintenance; 2) invasive assessment procedures are common in animals but very limited in humans; and 3) humans can describe how they feel in response to amino acid levels or balances, whereas animals cannot. New (pharmacologic) uses of amino acids have been and are being discovered (e.g.

Iodine toxicity and its amelioration.

Iodine (I) toxicity is rare in animals and humans, but nuclear explosions that give off radioactive I and excessive stable I ingestion in parts of the world where seaweed is consumed represent specialized I toxicity concerns. Chronic overconsumption of I reduces organic binding of I by the thyroid gland, which results in hypothyroidism and goiter. Bromine can replace I on position 5 of both T(3) and T(4) with no loss of thyroid hormone activity.

Oral iodine toxicity in chicks can be reversed by supplemental bromine.

Four chick bioassays were conducted to quantify iodine (I) toxicity and its amelioration in young chicks. A supplemental I level from KI of 600 mg/kg depressed growth in chicks fed methionine-deficient diets but not in those fed methionine-adequate diets. An I dose level >or= 900 mg/kg was required to cause growth depression in chicks fed a methionine-adequate corn-soybean meal diet.

The relative vitamin A value of 9-cis beta-carotene is less and that of 13-cis beta-carotene may be greater than the accepted 50% that of all-trans beta-carotene in gerbils.

The effectiveness of beta-carotene (betaC) as a vitamin A (VA) precursor may be influenced by the proportions of cis isomers of betaC consumed in the diet. Although the metabolic fates of cis isomers of betaC are poorly understood, their retinol equivalency has been assigned a value 50% that of all-trans (at) betaC. A dose-response design was used to estimate the relative VA value (VAV) of atbetaC, 9-cis (9c) betaC and 13-cis (13c) betaC in gerbils using total liver retinol as a measure of VAV.