Amino acid needs in horses.

The research paper discusses the needs and sources of essential and nonessential amino acids in horses, and how these needs can be met. Furthermore, it explores the various methods of assessing dietary amino acid adequacy in horses as well as their limitations.

Amino Acid Needs and Sources in Horses

• Amino acids in horses are divided into two types: essential amino acids, which cannot be synthesized in the body in sufficient amount and nonessential amino acids which can be synthesized in the horse’s body.
• Identifying a horse’s amino acid needs is crucial for creating the right dietary plan and reducing nitrogen losses to the environment.

Protein Digestibility and Measurement

• One method to identify these needs is to measure protein digestibility, which can be expressed as total tract digestibility or pre-cecal digestibility.
• Total tract digestibility covers absorption of nitrogen throughout the gastrointestinal tract, however, it doesn’t specify where it is absorbed or its source, whether from amino acids or other nitrogen sources.
• Pre-cecal digestibility signifies protein absorbed by the end of the ileum and is perceived as a more accurate measure of protein absorption in horses.

Assessing Dietary Amino Acid Adequacy

• Alternative methods to test dietary amino acid adequacy involve comparing the horse’s intake of amino acid versus a reference protein such as milk or muscle.
• This process can reveal limiting amino acids in the diet that are not present in the needed quantities to produce the reference protein.
• An ‘ideal’ protein for an animal is one where both the amino acid ratio and the quantities are correct for the animal’s needs.
• Another method of assessment is observing changes in average daily gain (ADGV), however, this can only be used in growing horses and needs a long observation period.
• Lastly, nitrogen retention can also indicate dietary adequacy, but the measurements involved can be complex and require animal confinement. These include calculating dietary nitrogen intake versus nitrogen losses in the form of hair, sweat, feces, and urine.
• Lastly, plasma concentrations of amino acids can be analyzed. A constant low concentration shows that the intake is below requirements.

Amino Acid Measurement Techniques

• In humans, the carbon oxidation technique is used for determining amino acid needs, which involves labeled amino acid isotopes being infused in the bloodstream and labeled exhaled carbon measurement. This technique strikes as a potentially efficient and precise method to measure amino acid needs in horses.
• Two measurements used in this technique are Direct Amino Acid Oxidation (DAAO) and Indirect Amino Acid Oxidation (IAAO).
• Both methods are anchored on the ideal protein concept.
• A recent study conducted by Tanner et al. used IAAO to measure protein synthesis in weanling horses.