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Lysine Requirements in Yearling Horses Determined Using Indicator Amino Acid Oxidation
K. L. Urschel
Department of Animal and Food Sciences
Protein is composed of amino acids and in order to ensure optimal rates of animal growth, each essential amino acid must be supplied in adequate amounts. In horses, lysine is the amino acid that is generally believed to limit rates of protein synthesis; however, the current dietary requirements for lysine have only been estimated based on lysine content of feed ingredients and have not been experimentally determined.
A cutting-edge technique known as the indicator amino acid oxidation (IAAO) method has been successfully used in other species, such as pigs and humans, to measure amino acid requirements and we hypothesize that this methodology will allow us to determine the lysine requirement of growing horses. The objective of this research is to validate and use the IAAO technique to determine the lysine requirement in growing (~12 month old) horses.
Six horses (12 - 14 months old) will be used in this study and each horse will be studied at each of six different levels of lysine intake, in six consecutive periods. Diets will consist of hay and a concentrate (grain) mixure and will include levels of lysine intake that are both higher and lower than the current dietary lysine recommendations. In each period, horses will be randomly assigned to a different level of lysine intake and will be allowed to adapt to the diet for 7 days before undergoing the IAAO procedures. Blood, breath and muscle samples will be taken during the IAAO procedures to measure amino acid oxidation (conversion to carbon dioxide) and rates of protein synthesis.
The basis for the IAAO methodology is that essential amino acids are either used for protein synthesis or, if they cannot be used for protein synthesis, degraded (oxidized). If one essential amino acid (in our case, lysine) is provided below its requirement level, it will limit the amount of protein synthesis that can occur, then all of the other amino acids will not be able to be used for protein synthesis and will be oxidized. If the intake of that essential amino acid (lysine) increases to above requirement levels, then it will no longer limit protein synthesis and there will be fewer other amino acids that are oxidized. By measuring the level of lysine intake needed to minimize the oxidation of the other amino acids, we will indirectly be measuring the amount of lysine needed to promote maximum rates of protein synthesis. This level of lysine intake will represent the lysine requirement. This research will be the first step towards determining amino acid requirements in horses, which will ultimately result in improved diet formulation for horses of all ages.
2010 Project Description
The sample collection portion of this research is scheduled to begin in May 2011. At this time, the diets have been formulated to allow for a range of lysine intakes of 80 - 145 mg/kg BW/day and we have worked with horses to adapt them to isotope infusion and breath sampling procedures. Sample collection will terminate in July 2011, and samples will be analyzed from August to December 2011. At that point in time, there will more tangible outputs (results and evidence of dissemination) to report.
There is one PhD student, Sara Tanner, that is working on this project and has already learned about the principles of the methodology and worked to formulate the diets. Additionally, 2 undergraduate students will also be involved in this study. There are no events, services or product outputs to report at this time.
Because we are just beginning the sample collection process, there are no impacts to report at this time. We do anticipate that the validation of the indicator amino acid oxidation methodology in horses will provide us with a valuable research tool to advance our knowledge of amino acid requirements in horses. Knowledge of the lysine requirements in yearlings will improve diet formulation for this age of horses.