Controlled trial of whole body protein synthesis and plasma amino acid concentrations in yearling horses fed graded amounts of lysine

• Published in: The veterinary journal (1997) 2016-10, Vol.216, p.93-100
• Main Authors: Mastellar, S.L., Coleman, R.J., Urschel, K.L.
• Format: Article
• Language: English
• Subjects: Amino acid; Amino Acids - blood; Amino Acids - metabolism; Animal Feed - analysis; Animals; Diet - veterinary; Dietary Supplements - analysis; Dose-Response Relationship, Drug; Equine; Horses - blood; Horses - metabolism; Indicator amino acid oxidation; Lysine; Lysine - administration & dosage; Muscles - chemistry; Protein Biosynthesis - drug effects; Protein synthesis
• ISSN: 1090-0233; 1532-2971
• DOI: 10.1016/j.tvjl.2016.07.007

•The effects of graded lysine intakes on whole body protein metabolism were studied in yearling Thoroughbred horses using [1-13C] phenylalanine infusion.•Plasma lysine concentrations increased with increasing lysine intake but the lysine requirement could not be determined.•Increasing lysine intake did not increase whole body protein synthesis at the range of lysine intakes studied.•Muscle concentrations of several amino acids were influenced by lysine intake.•The lysine requirement may have been lower than the lowest level of lysine intake or another amino acid may have been more limiting than lysine in the diet. Lysine has been reported as the first limiting amino acid in typical equine diets. Indicator amino acid oxidation (IAAO) has become the standard method for determining amino acid requirements in other species, but prior to this study, it has not been used to determine equine requirements. The aim of this study was to evaluate whole body protein synthesis and plasma and muscle amino acid concentrations in response to graded levels of lysine intake in yearling horses. Six Thoroughbred colts (358 ± 5 kg) were fed each of six treatment lysine intakes ranging from 76 to 136 mg/kg body weight/day. Blood samples were taken before and 90 min after the morning concentrate meal. Gluteal muscle biopsies were taken ~100 min after the morning concentrate meal. The next day, whole body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [13C] sodium bicarbonate followed by a 6 h primed, constant infusion of [1-13C] phenylalanine. Plasma lysine concentrations increased linearly (P