Thyroid Diseases.

Overview

• This article examines the characteristics, diagnosis, and treatment considerations for thyroid diseases in horses, highlighting the complexity of thyroid hormone fluctuations and their clinical implications in both adult horses and neonatal foals.

Thyroid Hormone Fluctuations in Horses

• Thyroid hormone levels in horses can vary due to external and internal factors such as:
• Time of day (circadian rhythms)
• Dietary influences
• Levels of physical activity
• Use of certain medications
• This variability can complicate the diagnosis of thyroid-related diseases because hormone levels alone may not reliably indicate disease status.

Hypothyroidism in Adult Horses

• True hypothyroidism, where the thyroid gland underproduces hormones, is rare in adult horses.
• When clinical signs suggest hypothyroidism, alternative causes should be considered, especially equine metabolic syndrome (EMS), which shares overlapping symptoms.
• EMS is characterized by insulin resistance, obesity, and laminitis, and may mimic or confound thyroid disease diagnosis.

Hyperthyroidism in Older Horses

• Hyperthyroidism, the condition of excessive thyroid hormone production, can occur, although less commonly, in older horses.
• It may present with distinct clinical signs such as weight loss, increased appetite, and behavioral changes.
• In some cases, these symptoms are severe enough to require surgical intervention to remove or reduce thyroid tissue.

Neonatal Foal Hypothyroidism

• Neonatal foals can present with congenital or developmental hypothyroidism, which is often linked to dysmaturity (prematurity or poor developmental progression).
• This form of hypothyroidism can be life-threatening without prompt diagnosis and management.
• Early intervention can improve outcomes and reduce mortality in affected foals.

Therapeutic Considerations

• Thyroid hormone supplementation may be used therapeutically to help manage EMS by potentially improving metabolic function.
• However, inappropriate or unjustified use of thyroid supplements can impair athletic performance by disrupting the horse’s normal hormonal balance.
• Careful assessment and tailored treatment plans are necessary to avoid adverse effects and ensure therapeutic efficacy.