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Why Horses May Bleed More in Winter Than Summer: Understanding Exercise-Induced Pulmonary Hemorrhage

Horses, like humans, can experience health issues that vary depending on the season. One puzzling phenomenon that horse owners and veterinarians often observe is the occurrence of more frequent nosebleeds in horses during the winter compared to the summer. This condition is commonly known as Exercise-Induced Pulmonary Hemorrhage (EIPH). While it can occur throughout the year, some factors make winter a potentially more challenging season for horses. In this article, we will explore why horses may bleed more in winter than summer, and what can be done to mitigate this issue.

Understanding EIPH

EIPH is a condition in which a horse experiences bleeding in the lungs during or after intense exercise. This can result in blood appearing in the horse's nostrils, a condition colloquially known as "bleeding" or "exercise nosebleeds." The exact cause of EIPH is not completely understood, but several factors contribute to its occurrence.

  1. Dry Air

One of the most significant reasons why EIPH is more prevalent in winter is the dry and cold air. In winter, the air is typically less humid, which can lead to increased respiratory discomfort for horses. Dry air can irritate the delicate lung tissues, making them more susceptible to damage during strenuous exercise. This irritation can lead to an increased risk of bleeding in the lungs.

2. Increased Exercise

Horses tend to be more active in the summer months, with longer days and better weather conditions encouraging more outdoor activities. During the winter, however, many horses may spend more time indoors and receive less exercise. When they are eventually taken out for more intense exercise in the winter, their bodies may be less conditioned, making them more prone to EIPH.

3. Hay and Bedding Dust

In the winter, horses often spend more time indoors in confined spaces, such as stalls and barns. The dust from hay and bedding can accumulate in these enclosed environments, leading to poor air quality. Inhaling this dusty air can further irritate the horse's respiratory system, making them more susceptible to EIPH.

4. Changes in Diet

Horses' diets may also change in the winter. They might receive more hay and less fresh pasture, leading to a potential increase in allergens and dust intake. These dietary changes can contribute to respiratory irritation and increase the risk of EIPH.

Preventing and Managing EIPH

Preventing and managing EIPH in horses is a multifaceted approach that involves several strategies:

  1. Improved Ventilation: Adequate ventilation in stables and barns can help reduce the accumulation of dust and improve air quality. This can minimize respiratory irritation.

  2. Humidification: Using humidifiers or water sprays in barns to increase indoor humidity can help alleviate the drying effect of cold air on the horse's respiratory system.

  3. Conditioning: Gradual and consistent exercise throughout the year can help condition the horse's lungs and reduce the risk of EIPH when intense workouts are required.

  4. Medications: Consultation with a veterinarian may lead to the use of medications, such as furosemide, to manage EIPH symptoms during the winter months.


While the exact cause of EIPH in horses is not completely understood, several factors contribute to the increased incidence of exercise-induced pulmonary hemorrhage in winter. Dry air, reduced exercise, dusty environments, and dietary changes all play a role in making horses more susceptible to bleeding during this season. By taking proactive steps to address these factors, horse owners and trainers can help mitigate the risk and discomfort associated with EIPH in their equine companions. If you suspect your horse is experiencing EIPH, it is essential to consult with a qualified veterinarian for proper diagnosis and treatment.

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