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MedicalDictionary.comThe Free Veterinary Medical Dictionary
Medical Condition🐕 Dogsendocrine

Canine Hypothyroidism

🗣️ Pronounced:hy-poh-THY-royd-izm
In One Sentence (Plain English)

An endocrine disorder in dogs caused by underactive thyroid glands that fail to produce adequate thyroid hormones.

Editorial Status: Verified from peer-reviewed veterinary sources (v1.0)
Updated: 2026-01-15

💬 In Plain English

The thyroid glands located in the neck control the body’s metabolic rate. In dogs, hypothyroidism happens when the immune system attacks the thyroid (lymphocytic thyroiditis) or the tissue slowly atrophies. As thyroid hormone levels drop, the dog’s metabolism slows down significantly. Dogs become sluggish, gain weight without eating more, seek warm spots because they feel cold, and lose fur along their tail (“rat tail”) and trunk.

🔬 Clinical & Technical Depth

For Vets & Technicians

Formal Clinical Definition

Deficiency of circulating thyroid hormones (primarily free and total thyroxine [T4] and triiodothyronine [T3]), resulting from immune-mediated lymphocytic thyroiditis or idiopathic thyroid follicular atrophy.

Why Veterinarians Use It

Veterinarians evaluate dogs for hypothyroidism when unexplained weight gain, lethargy, non-pruritic alopecia, or persistent skin and ear infections occur in middle-aged dogs.

Clinical Context Encountered

Commonly diagnosed in middle-aged dogs (4 to 10 years old) of medium-to-large breeds like Golden Retrievers, Doberman Pinschers, and Cocker Spaniels.

Clinical Reference Guide (Medical Condition)

Severity
Emergency StatusNon-Emergency Care
🚨 Red Flag Warnings (When to Contact an Emergency Vet)
  • •Myxedema coma is an extremely rare, severe complication of end-stage untreated hypothyroidism causing profound stupor, severe hypothermia, and bradycardia.

❓ Questions to Ask Your Veterinarian

Take these actionable questions with you to your next clinic visit or appointment:

  • 1Did the blood panel include a full thyroid panel (Total T4, Free T4 by equilibrium dialysis, and canine TSH)?
  • 2Could a concurrent illness be causing “euthyroid sick syndrome” (falsely low T4)?
  • 3What is the daily dosing schedule for synthetic levothyroxine (Thyro-Tabs)?
  • 4When should we recheck peak T4 levels (usually 4 to 6 hours post-pill)?

Academic & Clinical References