Endurance horse running with translucent overlay of blood cells and plasma volume.

Endurance Riding: Are Your Horse's Blood Values Telling the Whole Story?

Nico Varela in Health & Wellness December 2025 • 4 min read.

"Uncover how plasma volume shifts can mask crucial changes in your horse's hematocrit during endurance events, and how to get a clearer picture of their true physiological state."

Endurance riding tests the limits of a horse's stamina and speed, but pushing those limits can lead to dehydration and heat stress. Understanding how their body responds is crucial for success and safety. Changes in blood composition, particularly hematocrit, are closely monitored, but are these values always telling the whole story?

Increases in hematocrit, the percentage of red blood cells in the blood, are commonly seen during exercise. This is often attributed to splenic contraction (releasing more red blood cells) and fluid loss through sweat, which concentrates the blood. However, a simple rise in hematocrit might not reflect the complete picture of what's happening inside the horse.

This article delves into research investigating how changes in plasma volume, the liquid component of blood, can influence hematocrit and other blood values during endurance rides. By accounting for these shifts, we can gain a more accurate understanding of the physiological demands placed on horses in tropical endurance conditions and potentially refine monitoring strategies.

The Plasma Volume Puzzle: Why Corrected Values Matter

Endurance horse running with translucent overlay of blood cells and plasma volume.

The study meticulously tracked Arabian horses competing in endurance rides, monitoring blood values before, during, and after the races. Researchers considered factors like erythrocyte and leukocyte counts, hemoglobin concentration, hematocrit, total protein, and key biochemical markers. What sets this research apart is its use of a mathematical approach to correct for changes in plasma volume.

The key is that sweating during endurance events causes significant fluid loss, reducing plasma volume. This reduction concentrates the blood, artificially inflating hematocrit and other values. By calculating the percentual change in plasma volume, researchers could adjust the measured blood values, revealing a different pattern of physiological response.

Traditional View: A rise in hematocrit during exercise indicates increased oxygen-carrying capacity.
Plasma Volume Corrected View: When plasma volume shifts are considered, hematocrit may actually decrease during the ride, suggesting red blood cells are being redistributed.

This distinction is critical. While a simple increase in hematocrit might seem positive, the corrected data suggests a more complex scenario where the horse's body is actively managing blood cell distribution during the intense effort. Failing to account for plasma volume could lead to misinterpretations of the horse's condition and potentially impact management decisions.

Beyond the Numbers: A More Nuanced Approach to Horse Care

This research highlights the importance of looking beyond simple blood values when assessing a horse's condition during endurance events. Accounting for plasma volume changes provides a more nuanced understanding of the physiological demands and can help prevent misinterpretations.

The study suggests that during endurance rides, red blood cells may be redistributed within the horse's body, and plasma proteins might be consumed for energy. These insights could lead to refined training and management strategies, optimizing performance and minimizing the risk of overexertion.

By adopting a more comprehensive approach to monitoring, incorporating plasma volume considerations, horse owners and veterinarians can better support the health and well-being of these incredible equine athletes.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1590/s0100-736x2012000900023, Alternate LINK

Title: Do Hematologic Constituents Really Increase Due To Endurance Exercise In Horses?

Subject: General Veterinary

Journal: Pesquisa Veterinária Brasileira

Publisher: FapUNIFESP (SciELO)

Authors: Antonio R. Teixeira-Neto, Guilherme C. Ferraz, Augusto R.C. Moscardini, Raquel M. Albernaz, Milena R. Gondin, Antonio Queiroz-Neto

Published: 2012-09-01

Everything You Need To Know

What is hematocrit, and why is it important in endurance riding?

Hematocrit is the percentage of red blood cells in the blood, and it is commonly monitored in horses during endurance riding. Typically, an increase in hematocrit is observed during exercise due to splenic contraction and fluid loss through sweat, concentrating the blood. However, the significance of hematocrit must be considered in the context of plasma volume changes.

What is plasma volume, and how does it change during endurance rides?

Plasma volume is the liquid component of blood. During endurance rides, horses lose significant amounts of fluid through sweating, which reduces plasma volume. This reduction concentrates the blood, affecting the hematocrit and other blood values. Researchers use mathematical approaches to correct for these changes, providing a more accurate understanding of the horse's physiological state.

Why is it important to account for plasma volume changes in a horse's blood values?

Accounting for plasma volume changes is crucial because it offers a more accurate picture of a horse's condition during endurance events. Without this, the observed changes in hematocrit might be misinterpreted. For example, a simple increase in hematocrit might seem positive, but when corrected for plasma volume, it may reveal a decrease, suggesting a redistribution of red blood cells. This correct approach prevents misinterpretations of the horse's health, allowing for better management and care decisions.

What are the implications of not considering plasma volume changes in assessing a horse's health?

The shift in plasma volume is significant because it can lead to misinterpretations of the horse's health. During endurance rides, the loss of plasma volume through sweating artificially inflates hematocrit. If not corrected, this can lead to an inaccurate assessment of the horse's condition. By correcting for plasma volume, a more accurate understanding of the horse's physiological response is achieved, helping to prevent potentially harmful decisions regarding the horse's care.

How did the study assess the effects of endurance riding on horses' blood values, and what approach was used to correct for plasma volume changes?

The study tracked Arabian horses during endurance rides, monitoring blood values before, during, and after races. They measured erythrocyte and leukocyte counts, hemoglobin concentration, hematocrit, total protein, and key biochemical markers. The study corrected for plasma volume changes to provide a more accurate assessment of the physiological demands placed on horses and refine monitoring strategies. This included the use of a mathematical approach to adjust measured blood values, offering a different view of the physiological responses compared to traditional methods that do not account for plasma volume changes.