Effects of dietary amino acid supplementation on measures of whole-body and muscle protein metabolism in aged horses.

The study aimed at understanding the impact of supplemental amino acids on the metabolism of protein in older horses. It found that while there were some changes in protein degradation, overall body protein metabolism was not significantly improved by the supplements.

Research Methodology

• The research conducted employed a replicated Latin square design, which is a design used in experiments, most commonly agricultural ones, where the goal is to control two sources of variance. The researchers studied six old horses that were approximately 20 years of age.
• Each of the six horses were subjected to three identical calorie and nitrogen diets with varying amounts of certain amino acids like lysine, threonine and methionine. These amino acids are known for their roles in protein synthesis.
• For every 15-day period, urine and faeces samples were collected from the horses to assess the nitrogen balance. Blood samples were also collected before and after the horses were fed both for the analysis of plasma urea nitrogen (PUN), glucose, insulin, and concentration of plasma amino acids. Skeletal muscle samples were harvested for measurement of proteins that play a role in muscle protein synthesis and degradation.
• The researchers used stable isotope infusion procedures to make comparisons of the whole-body rates of protein synthesis and degradation across the different diets.

Results and Findings

• The researchers observed no effect of the different diets on the relative abundance of proteins involved in protein synthesis, nitrogen retention or phenylalanine kinetics.
• The PUN concentrations were higher in horses on the LYS/THR and LYS/THR/MET diets than the ones on the CON diet. This could potentially be associated with an increase in protein catabolism, which refers to the breakdown of proteins into simpler compounds.
• Atrogin-1 abundance which is a marker of muscle protein breakdown, was found to be higher for the CON diet in the post-absorptive state of the horses. This result suggested that amino acid supplementation resulted in less muscle protein degradation when horses had finished absorbing their nutrients.
• However, there were no differences in nitrogen retention and phenylalanine kinetics between the three diets. This led the researchers to conclude that while the supplements influenced some biochemical markers, they did not result in a general improvement in whole-body protein metabolism.
• Furthermore, the higher PUN concentrations in horses on the supplemental diets suggested that the additional amino acids may have been catabolized or broken down, rather than used for protein synthesis.
• The researchers concluded their study with the finding that amino acid availability was not limiting protein synthesis in the sedentary and aged horses while on the CON diet.