Splanchnic extraction of phenylalanine in mature mares was not affected by threonine supplementation.

Summary

Threonine plays an important role in intestinal health and immune function in horses, yet its metabolic interactions with other amino acids remain poorly characterised. Mastellar and colleagues investigated whether increasing dietary threonine intake (from 58 to 119 mg/kg/day) altered how the splanchnic tissues (primarily the gut and liver) extract phenylalanine—a key indicator amino acid—using stable isotope methodology in six mature Thoroughbred mares studied across both oral and intravenous infusion protocols. Splanchnic phenylalanine extraction remained consistent at approximately 26–27% regardless of threonine supplementation status, suggesting that threonine availability does not significantly influence first-pass amino acid metabolism in mature horses. These baseline extraction values are particularly valuable for future research employing the indicator amino acid oxidation technique, which relies on precise estimates of splanchnic amino acid handling to assess protein quality and amino acid requirements. For practitioners involved in equine nutrition, this finding indicates that moderate threonine supplementation strategies can be evaluated independently without expecting secondary effects on the bioavailability of other essential amino acids at the splanchnic level.

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Key Findings

• •Splanchnic extraction of phenylalanine was not significantly affected by threonine supplementation (P > 0.05)
• •Phenylalanine extraction rates were 26 ± 5% for high threonine diet and 27 ± 3% for basal diet
• •Phenylalanine kinetics remained stable across dietary threonine intakes ranging from 58 to 119 mg/kg/day
• •These standardized values improve accuracy of future equine indicator amino acid oxidation studies

Conditions Studied

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