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Unlocking the Equine Enigma: Tie-Up in Mares and Low Thyroxine Levels

Updated: Sep 14, 2023

Horses are fascinating creatures, known for their strength, agility, and grace. Yet, like any other living being, they are not immune to health issues. One such concern that often plagues mares is a condition known as "tie-up," or exertional rhabdomyolysis. In recent years, researchers have made a noteworthy connection between tie-up in mares and low thyroxine levels, shedding light on a previously overlooked aspect of equine health. In this blog, we will delve into this intriguing relationship and discuss why supplementing thyroxine is important for the well-being of mares.

Understanding Tie-Up in Mares

Tie-up, or exertional rhabdomyolysis, is a condition that causes severe muscle cramping and stiffness in horses, often triggered by exercise or stress. It is characterized by muscle cell damage and the release of enzymes and proteins into the bloodstream, leading to pain, weakness, and potential long-term damage. This condition can be challenging for both the horse and its owner, as it can hinder performance, cause discomfort, and even lead to serious complications if left untreated.

The Thyroid Connection

Recent research has unveiled an intriguing connection between low thyroxine levels and tie-up in mares. Thyroxine, also known as T4, is a crucial thyroid hormone responsible for regulating the body's metabolism. In mares, low thyroxine levels have been linked to an increased risk of developing tie-up episodes. Here's why this relationship is significant:

  1. Metabolic Regulation: Thyroxine plays a vital role in maintaining a horse's metabolic balance. Low levels of this hormone can disrupt the horse's ability to efficiently utilize energy, leading to metabolic imbalances that may contribute to muscle issues.

  2. Muscle Function: Thyroxine also affects muscle function directly. When thyroxine levels are suboptimal, it can lead to muscle weakness and cramping, making the horse more susceptible to tie-up.

  3. Increased Susceptibility: Mares with low thyroxine levels are at a higher risk of experiencing tie-up episodes, particularly during strenuous exercise. Identifying and addressing low thyroxine levels can help prevent these episodes from occurring.

Supplementing Thyroxine: Why It Matters

Given the evident link between low thyroxine levels and tie-up in mares, supplementing thyroxine has become an important aspect of equine care. Here's why it matters:

  1. Improved Performance: Supplementing thyroxine in mares with low levels can lead to enhanced performance. With improved muscle function and better metabolic regulation, horses are better equipped to handle the physical demands of training and competition.

  2. Reduced Risk of Tie-Up: By addressing the root cause of tie-up, low thyroxine levels, supplementation can significantly reduce the risk of future episodes. This means fewer instances of pain, discomfort, and potential long-term damage for your mare.

  3. Enhanced Quality of Life: Ensuring your mare's thyroxine levels are within a healthy range not only benefits her performance but also contributes to her overall well-being. A horse free from the constraints of tie-up is a happier, healthier animal.

Consulting with a Veterinarian

It's important to note that supplementing thyroxine should not be done without consulting a veterinarian. Determining the appropriate dosage and monitoring the mare's thyroid levels regularly are critical steps in this process. A veterinarian will conduct blood tests to assess thyroxine levels and recommend the most suitable course of action based on the individual needs of the horse.


The connection between tie-up in mares and low thyroxine levels is a fascinating discovery in the world of equine health. By understanding this relationship and addressing low thyroxine levels through supplementation under the guidance of a veterinarian, horse owners can help their mares lead healthier, more fulfilling lives. A horse that is free from the constraints of tie-up is a horse that can truly thrive.

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