title: Dietary crude protein intake influences rates of whole-body protein synthesis in weanling horses.
abstract: The objective of this study was to measure whole-body protein kinetics in weanling horses receiving forage and one of two different concentrates: (1) commercial crude protein (CCP) concentrate, which with the forage provided 4.1 g CP/kg bodyweight (BW)/day (189 mg lysine (Lys)/kg BW/day), and (2) recommended crude protein (RCP) concentrate which, with the same forage, provided 3.1 g CP/kg BW/day (194 mg Lys/kg BW/day). Blood samples were taken to determine the response of plasma amino acid concentrations to half the daily concentrate allocation. The next day, a 2 h-primed, constant infusion of [(13)C]sodium bicarbonate and a 4 h-primed, constant infusion of [1-(13)C]phenylalanine were used with breath and blood sampling to measure breath (13)CO2 and blood [(13)C]phenylalanine enrichment. Horses on the CCP diet showed an increase from baseline in plasma isoleucine, leucine, lysine, threonine, valine, alanine, arginine, asparagine, glutamine, ornithine, proline, serine, and tyrosine at 120 min post-feeding. Baseline plasma amino acid concentrations were greater with the CCP diet for histidine, isoleucine, leucine, threonine, valine, asparagine, proline, and serine. Phenylalanine, lysine, and methionine were greater in the plasma of horses receiving the RCP treatment at 0 and 120 min. Phenylalanine intake was standardized between groups; however, horses receiving the RCP diet had greater rates of phenylalanine oxidation (P = 0.02) and lower rates of non-oxidative phenylalanine disposal (P = 0.04). Lower whole-body protein synthesis indicates a limiting amino acid in the RCP diet.
authors: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40506, USA.
authors: S L
authors: SL
authors: Tanner
authors: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40506, USA.
authors: A L
authors: AL
authors: Wagner
authors: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40506, USA.
authors: R N
authors: RN
authors: Digianantonio
authors: Equine Studies Group, WALTHAM Centre for Pet Nutrition, Melton Mowbray, UK.
authors: P A
authors: PA
authors: Harris
authors: Buckeye Nutrition, Dalton, OH 44618, USA.
authors: J T
authors: JT
authors: Sylvester
authors: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40506, USA. Electronic address: klurschel@uky.edu.
authors: K L
authors: KL
authors: Urschel
mesh_terms: D000596:Amino Acids / Q000097:blood; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000378:metabolism*; D006736:Horses / Q000254:growth & development / Q000378:metabolism*; D014176:Protein Biosynthesis; D014886:Weaning
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins
keywords: Amino acids; Horse; Phenylalanine kinetics; Protein intake; Protein synthesis