Thyroid hormones may be small, but their impact on your pet’s health is huge. Whether underactive (hypothyroidism) or overactive (hyperthyroidism), thyroid dysfunction can drastically affect your pet’s metabolism, energy, and overall well-being.

At Milford Animal Hospital, we specialize in identifying and treating these common endocrine disorders in both dogs and cats. Early intervention, personalized treatment, and long-term monitoring can make all the difference in your pet’s quality of life.

What Are Thyroid Disorders?

The thyroid gland produces hormones that regulate the body’s metabolic rate. When thyroid function is disrupted, it causes widespread effects:

  • Hypothyroidism: Too little thyroid hormone → slowed metabolism
  • Hyperthyroidism: Too much thyroid hormone → accelerated metabolism

Understanding Hypothyroidism in Dogs

What It Is

Hypothyroidism is most common in middle-aged to older dogs. It occurs when the thyroid gland doesn’t produce enough hormones, leading to a sluggish metabolism.

Common Causes

  • Lymphocytic thyroiditis (autoimmune)
  • Idiopathic atrophy of thyroid tissue
  • Rare causes: tumors, iodine deficiency, congenital issues

Symptoms to Watch For

  • Weight gain without increased appetite
  • Lethargy, fatigue, low exercise tolerance
  • Dry, thinning coat and hair loss (esp. tail and flanks)
  • Cold intolerance—seeking warmth or shivering
  • Recurrent skin or ear infections

Explore Canine Hypothyroidism – Cornell Vet

Understanding Hyperthyroidism in Cats

What It Is

Hyperthyroidism most often affects senior cats. It’s caused by an overactive thyroid gland—typically due to a benign adenoma (non-cancerous tumor).

Common Causes

  • Thyroid adenomas (95% of cases)
  • Carcinoma (rare, malignant)
  • Environmental and dietary factors may also play a role

Symptoms to Watch For

  • Weight loss despite a ravenous appetite
  • Hyperactivity, restlessness, vocalization
  • Vomiting or diarrhea
  • Increased thirst and urination
  • Rapid heartbeat or arrhythmias

Learn more about Hyperthyroidism in Cats – Cornell Feline Health Center
AAHA Guidelines for Feline Hyperthyroidism

Why Thyroid Disorders Matter

In Dogs with Hypothyroidism

Untreated, this condition can lead to:

  • Obesity
  • Heart disease
  • Skin infections
  • Neurological changes
  • Infertility

In Cats with Hyperthyroidism

Unmanaged cases may cause:

  • Hypertension (high blood pressure)
  • Heart disease (thyrotoxic cardiomyopathy)
  • Kidney damage
  • Sudden blindness or seizures

How We Diagnose Thyroid Issues

Hypothyroidism

  • Total T4 (thyroxine) and TSH levels are assessed via blood test
  • Confirmatory tests may include free T4, thyroid autoantibodies, or ultrasound/biopsy

Hyperthyroidism

  • Elevated T4 is the primary diagnostic indicator
  • Additional testing may include blood pressure, kidney function, and thyroid imaging to rule out carcinoma or plan for radioactive iodine therapy

Routine wellness exams are key. Here’s why regular veterinary visits matter, especially for senior pets.

Treatment Options at Milford Animal Hospital

For Hypothyroidism in Dogs

  • Oral thyroid hormone replacement (levothyroxine)
  • Regular follow-up bloodwork to adjust dosage and monitor levels

For Hyperthyroidism in Cats

  • Methimazole: Oral or transdermal medication to reduce hormone production
  • Radioactive iodine (I-131): Curative treatment that destroys overactive thyroid tissue
  • Surgery: Removal of the affected thyroid gland, used selectively
  • Prescription diets (e.g., iodine-restricted foods) for mild cases

Living with a Thyroid Condition: Long-Term Management

Pets with thyroid disease can live full, happy lives with appropriate management.

  • Lifelong monitoring is essential. Thyroid levels should be rechecked every 6–12 months.
  • Routine lab work also screens for related conditions such as kidney disease in hyperthyroid cats or high cholesterol in hypothyroid dogs.
  • Senior pets need extra care—preventive testing and age-appropriate care help avoid complications.

When to Call the Vet

Contact us if you notice:

  • Unexplained weight changes
  • Changes in appetite or behavior
  • New skin problems
  • Increased thirst or restlessness in older cats

Milford Animal Hospital is here to help with diagnostics, treatment, and ongoing support tailored to your pet’s specific needs.

Key Takeaways

  • Thyroid hormones play a major role in metabolism and organ health
  • Hypothyroidism is common in middle-aged dogs; hyperthyroidism affects senior cats
  • Routine screening helps catch disease early and avoid complications
  • With proper care, pets with thyroid disorders can thrive

If your pet is due for wellness bloodwork or showing possible signs of thyroid imbalance, contact Milford Animal Hospital to schedule an exam. We’re committed to helping your pet stay healthy, happy, and active—at every life stage.