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Equine veterinary journal2023; doi: 10.1111/evj.13981

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals.

Abstract: Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.
© 2023 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2023-08-03 PubMed ID: 37533378DOI: 10.1111/evj.13981Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Introduction:

  • Equine thyroid disorders: Disorders of the thyroid gland in horses.
  • Diagnostic challenge: It’s difficult to diagnose thyroid disorders in horses due to:
    1. Effects of nonthyroidal factors: Other factors outside the thyroid can influence the system that controls thyroid hormone production (known as the hypothalamic-pituitary-thyroid axis).
    2. Horses’ tolerance: Horses can handle a wide range of thyroid hormone levels and can even survive without a thyroid gland.

Types of Disorders:

  • Benign thyroid tumors: These are non-cancerous growths on the thyroid gland and are common in older horses.
  • Primary hypothyroidism or hyperthyroidism: These are conditions where the thyroid gland produces too little (hypo) or too much (hyper) thyroid hormone. They’re rare in adult horses.
  • Congenital hypothyroidism: This is a condition where foals (baby horses) are born with an underactive thyroid. It’s also rare.

Misunderstandings:

  • There’s a misconception about hypothyroidism in adult horses. In dogs and humans, hypothyroidism is associated with obesity, tiredness, and poor performance. People mistakenly think it’s the same in horses.
  • Low levels of thyroid hormones in horses are often seen as a result of other medical or metabolic issues. These low levels don’t necessarily mean the horse has hypothyroidism.

Assessing Thyroid Function:

  • To evaluate how the horse’s thyroid is functioning, one can measure the levels of thyroid hormones in the blood. These hormones are:
    1. Thyroxine (T4)
    2. Triiodothyronine (T3)
  • However, interpreting these results is tricky because:
    1. Pulsatile secretion: Thyroid hormones are released in bursts.
    2. Many factors: Various elements can influence the hormone levels.
  • Dynamic testing, like the thyrotropin-releasing hormone stimulation test, can help understand how the thyroid gland reacts to stimuli.

Treatment and Supplementation:

  • True hypothyroidism is very rare in horses.
  • However, thyroid hormone supplementation (using T4) is often given to horses, especially to manage obesity and performance issues.

Conclusion:

This review delves into the workings of the thyroid gland in adult horses and foals, how to interpret blood thyroid hormone levels, and how to evaluate horses with potential thyroid problems. It also discusses the use of T4 supplementation in horse treatment.

In simpler terms, while thyroid disorders in horses are hard to diagnose and are often misunderstood, it’s essential to approach them with care. This review helps clarify the complexities surrounding equine thyroid disorders and their treatment.

Cite This Article

APA
Bertin FR, Frank N, Breuhaus BA, Schott HC, Kritchevsky JE. (2023). Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals. Equine Vet J. https://doi.org/10.1111/evj.13981

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Bertin, François-René
  • School of Veterinary Science at The University of Queensland, UQ Gatton Campus, Gatton, Queensland, Australia.
Frank, Nicholas
  • College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA.
Breuhaus, Babetta A
  • College of Veterinary Medicine at North Caroline State University, Raleigh, North Carolina, USA.
Schott, Harold C
  • College of Veterinary Medicine at Michigan State University, East Lansing, Michigan, USA.
Kritchevsky, Janice E
  • College of Veterinary Medicine at Purdue University, West Lafayette, Indiana, USA.

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Citations

This article has been cited 1 times.
  1. Stoeckle SD, Stage HJ, Gehlen H. Thyroid Disease in Horses-Retrospective Case Series on Patients Examined for Thyroid Disease in an Equine University Clinic (2009-2024). Vet Sci 2025 Nov 27;12(12).
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