# Concentration Changes in Plasma Amino Acids and Their Metabolites in Eventing Horses During Cross-Country Competitions

## TL;DR

This study tracks changes in amino acid levels in eventing horses before, during, and after cross-country competitions to understand how their bodies respond to intense exercise.

## Contribution

The study identifies specific amino acid and metabolite fluctuations in eventing horses after high-intensity exercise, offering insights into potential biomarkers for performance and recovery.

## Key findings

- 21 out of 23 plasma amino acids increased after exercise, while cysteine decreased.
- Proline levels remained elevated and glycine decreased the morning after exercise.
- Ammonia and urea levels increased after exercise and stayed elevated the next morning.

## Abstract

Eventing horses are exposed to intense physical stress during the cross-country test. Amino acids play key roles in energy metabolism and muscle recovery. This study examines the changes in 23 plasma amino acid concentrations and two related metabolites (ammonia and urea) in twenty horses, before and after cross-country exercise at international competitions. Blood samples were obtained before, as well as at 10 and 30 min after exercise and on the next morning. Our results showed that plasma concentration levels for 21 out of the 23 amino acids examined increased after exercise, while cysteine levels decreased. Moreover, 21/23 plasma amino acid levels returned to baseline the next morning, while the concentration of proline stayed elevated, and that of glycine decreased. Ammonia and urea levels increased after exercise and remained elevated during the following morning. This study demonstrates that longitudinal changes in plasma amino acid concentrations occur at specific time points following cross country exercise in eventing horses.

Plasma amino acid (PAA) concentration in horses vary according to the exercise type. This study evaluated the changes in PAA levels and the associated metabolites, urea and ammonia, following short-duration, high-intensity cross-country exercise in eventing horses. Twenty eventing horses participated in 55 rides at 14 international competitions (2* to 4* levels) across five venues in Germany and Poland. Blood samples were collected at four timepoints: before exercise (TP0), at 10 min (TP1), and at 30 min (TP2) post-exercise, as well as in the morning on the day after the competition (TP3). A total of 23 different PAAs and two metabolites (ammonia and urea) were analyzed. PAA concentration difference over time was assessed by a mixed ANOVA. Significant fluctuations were observed in 18/25 parameters. For 21/23 PAAs, levels increased at TP1 and/or TP2, while cysteine concentrations decreased. Concentrations returned to pre-competition levels for 21/23 PAAs by TP3. Proline levels remained elevated (p = 0.002), while those of glycine significantly decreased (p = 0.027) at TP3. Plasma ammonia and urea levels increased at TP1, TP2 and TP3. This study provides foundations for supplementation strategies and can inform future works exploring PAAs’ role in performance and training adaptation in eventing horses and their potential as performance-related biomarkers.