What is plasma myeloperoxidase (MPO) and why is it relevant in equine fitness?

Plasma myeloperoxidase (MPO) is a key indicator used to assess neutrophil degranulation and disruptions in the oxidant/antioxidant balance in horses. It's relevant because its concentration changes in response to exercise and training duration, offering insights into a horse's physiological response to training. This information can be crucial for assessing fitness and readiness for competition, helping owners and trainers make informed decisions about training regimens and competition schedules.

How does training duration affect plasma MPO concentrations in Thoroughbred racehorses?

The study indicated that plasma MPO concentration increased at all sampling points (before, during, and after exercise) as training duration progressed. This means that as the horses underwent longer training periods (beginning, middle, and end of a nine-month period), their MPO levels increased in response to exercise. This suggests a direct correlation between training duration and the horse's physiological response, making MPO a potentially useful marker for tracking fitness.

Were there any differences observed in plasma MPO levels between elite and non-elite horses?

No, the study found no significant differences in plasma MPO concentration between elite and non-elite horses. This suggests that the effect of exercise and training duration on MPO levels is similar regardless of the horse's performance level. This finding is important because it implies that MPO could be a universally applicable marker for assessing fitness across different levels of equine athletes.

Besides plasma MPO, what other biological markers were measured, and how did they respond to exercise?

Besides plasma MPO concentration, researchers measured white blood count (WBC), neutrophil count (Neut), lymphocyte count, and neutrophil percentage (%Neut). WBC increased above baseline at all measured points. Neut and %Neut increased 4 hours post-exercise, influenced by training duration. These markers, along with MPO, provide a comprehensive view of the horse's physiological response to exercise and training, particularly focusing on inflammatory and oxidative stress responses.

How can the findings on plasma MPO be applied to optimize a horse's training and enhance performance?

By monitoring plasma MPO levels, trainers and owners can gain a better understanding of how their horses are adapting to training. The study indicates that MPO is influenced by both exercise and training duration. By tracking these levels, one can tailor training regimens, adjust the intensity of workouts, and optimize recovery periods. Furthermore, understanding MPO levels helps in making informed decisions about competition schedules, ensuring horses are adequately prepared and reducing the risk of overtraining or injury. The study underscores the need for further research into MPO as a practical tool in equine sports medicine to fine-tune training programs.

Thoroughbred racehorse on a treadmill with MPO data visualization

Is Your Horse Fit to Race? How Training Affects Key Performance Markers

Lena Voss in Health & Wellness December 2025 • 5 min read.

"Unlocking the secrets of equine fitness: A deep dive into how training duration impacts myeloperoxidase levels and overall performance in Thoroughbred racehorses."

For horse owners and enthusiasts, understanding the intricacies of equine fitness is paramount. Exercise triggers a cascade of physiological changes in horses, including the induction of oxidant/antioxidant processes. Among the markers of interest, plasma myeloperoxidase (MPO) has emerged as a key indicator. Plasma MPO concentration is often used to assess neutrophil degranulation and disruptions in the oxidant/antioxidant balance. However, the effect of training on these responses remains an area of ongoing investigation.

A recent study published in Comparative Exercise Physiology sought to evaluate how training impacts plasma MPO concentrations in Thoroughbred racehorses. By measuring MPO levels at various time points before and after intense exercise, researchers aimed to uncover the relationship between MPO concentration, physiological measurements, and overall performance. The findings offer valuable insights into assessing fitness and readiness for competition.

This trending article translates the complex research into actionable advice for horse owners, trainers, and enthusiasts. We will explore how exercise and training duration affect plasma MPO concentrations, and how this information can be used to optimize training regimens and enhance performance.

How Does Exercise Impact MPO Levels in Horses?

Thoroughbred racehorse on a treadmill with MPO data visualization

The study, conducted with 26 Thoroughbred racehorses, involved an exercise test on a high-speed treadmill. The horses were assessed at three distinct phases of a nine-month training period: the beginning (first three months), the middle (second three months), and the end (last three months). Throughout these periods, researchers monitored key indicators, including heart rate, speed, and distance covered. Additionally, blood samples were collected at specific intervals: before exercise (To), during maximal speed (Tvmax), 5 minutes post-exercise (T5min), and 4 hours post-exercise (T4h). These samples were analyzed to determine plasma lactate, serum creatine kinase concentration, plasma MPO concentration, white blood count (WBC), neutrophil count (Neut), lymphocyte count, and neutrophil percentage (%Neut).

The results revealed several significant changes in response to exercise. For instance, WBC increased above To values at all sampling points, regardless of training duration. Similarly, Neut and %Neut increased above To values at T4h. Interestingly, as the duration of training progressed, values at Tvmax, T5min, and T4h increased. Plasma MPO concentration also increased above To values at all sampling points, with all values rising as training duration increased. However, training intensity (number of fast work sessions) did not affect any of the measurements, and no correlations were identified between biological markers (including MPO) and physiological/training measurements.

WBC Count: Increased above baseline at all measured points.
Neutrophil Count: Increased 4 hours post-exercise, influenced by training duration.
Plasma MPO: Increased at all points, correlated with training duration.
Training Intensity: Had no significant impact on the measured values.

Elite versus Non-Elite Horses: The study also examined differences between elite and non-elite horses. Surprisingly, no significant differences were found between the two groups, suggesting that plasma MPO concentration is similarly affected by exercise and training duration regardless of performance level. These findings indicate that plasma MPO concentration is influenced by both exercise and training duration, warranting further investigation as a potential tool for assessing fitness and readiness for competition.

What Does This Mean for Your Horse's Training?

The study underscores the importance of considering training duration when evaluating equine fitness. Plasma MPO concentration is clearly affected by exercise and training, indicating that it could serve as a valuable marker for assessing a horse's response to training. Further research is needed to explore the potential of plasma MPO as an indicator of fitness and readiness for competition. By monitoring MPO levels, trainers and owners may gain a better understanding of how their horses are adapting to training, allowing for more informed decisions about training regimens and competition schedules. Keep in mind, the intensity and recovery between these intense bouts is also paramount to ensuring a healthy and performing animal. This study provides a foundation for future investigations into the use of plasma MPO as a practical tool in equine sports medicine.