An underactive thyroid slows a dog’s whole body down. Weight creeps up on the same food, energy drops, the coat thins, and the dog starts seeking warm spots. In autumn, these changes are easy to blame on shorter walks and colder weather. An examination and blood tests, read together, can tell the difference.
What the thyroid does
The thyroid is a small gland in the neck that makes hormones controlling how fast the body burns energy. When it produces too little, everything runs slower: metabolism, hair growth, skin renewal, even the heart rate. The most common cause in dogs is the immune system gradually damaging the gland, which is why signs creep in over months rather than appearing overnight.
It is one of the most common hormonal conditions in dogs, and it usually appears in middle age. Medium and large breeds are over-represented, including golden retrievers, Labradors, Dobermans, boxers and cocker spaniels, though any dog can be affected. Cats rarely develop it on their own. Older cats tend to have the opposite problem, an overactive thyroid.
Why autumn makes it easy to miss
Several of the classic signs look like seasonal changes, which is exactly why they are missed. A dog who is heavier in October is assumed to be walking less. A dog who lies on the heat register is assumed to be cold like everyone else. A dull coat is blamed on the rain. Taken together, though, those changes form a pattern worth checking.
The signs to look for
- Weight gain without eating more, or difficulty losing weight on a sensible diet
- Low energy: sleeping more, lagging on walks, less interest in play
- Seeking heat and seeming bothered by cold weather
- Coat changes: thinning hair on the sides, a bare or thin tail, a dull or greasy coat, or fur that is slow to grow back after clipping
- Skin changes: flaking, darkened patches, and skin or ear infections that keep coming back
- A slower, more subdued dog overall, which families often describe as “just getting older”
No single sign proves anything. Plenty of dogs gain weight in autumn for ordinary reasons, and our guide to healthy weight for dogs and cats in Langley covers those. But weight gain alongside lethargy, heat seeking and coat changes deserves a blood test.
How it is diagnosed
Diagnosis starts with an examination and a history of what you have noticed, then blood work through our diagnostics service. We usually look at more than one thyroid value, because a single low reading can be misleading. Other illnesses, and some products a dog receives for unrelated reasons, can temporarily lower thyroid levels, so results are always read alongside the whole picture.
It helps to bring a list of what you have noticed and roughly when each change began, along with your dog’s food, snacks and daily exercise. Photos of the coat from a year ago can be surprisingly useful, because gradual thinning is hard to judge from memory. Ask when you book whether your dog should skip breakfast, since some of the other blood tests run at the same visit are clearer on an empty stomach.
A general blood panel is often run at the same time. Hypothyroidism can raise cholesterol, and the panel also helps rule out other causes of the same signs.
What happens next
When a dog is diagnosed, the missing hormone can be replaced with daily supplementation for life, and our medical services team fine-tunes the amount with follow-up blood tests. Many dogs regain energy within a few weeks. Coat and skin take longer, often a few months, as new hair grows in. Tell us if your dog becomes restless, pants more, drinks a lot more or starts losing weight quickly once supplementation begins, since those can be signs the amount needs adjusting.
Weight usually starts to come down once the thyroid is balanced, and our nutrition counselling team can help set a realistic target and portion plan so the loss is steady rather than sudden.
Please do not give your dog any thyroid product or supplement bought online or meant for people. The amount has to match your dog, and getting it wrong causes its own problems.
Checking regularly
Because the signs creep in slowly, routine check-ups and blood work can pick up early clues, such as raised cholesterol or gradual weight and coat changes, that prompt a closer look. Our wellness program visits are a natural time to discuss screening, especially for breeds at higher risk.
Frequently asked questions
Will my dog need this for life?
Yes, in almost every case. The gland does not recover, but the condition is very manageable, and most dogs live a normal, active life once their hormone level is balanced and monitored.
My dog is overweight. Does that mean a thyroid problem?
Not usually. Most weight gain comes from food and exercise. A thyroid problem becomes more likely when weight gain comes with low energy, heat seeking and coat or skin changes.
How often will my dog need blood tests?
More often at the start, while the amount is being adjusted, then usually once or twice a year once things are stable. We will set a schedule for your dog.
Is it painful for my dog?
It is not painful in itself, but a dog with low thyroid often feels sluggish and uncomfortable in the cold, and recurring skin and ear infections can be sore. Most owners notice their dog brightens once it is managed.
Can my cat get it?
It is rare for cats to develop it naturally. Older cats far more often have an overactive thyroid, with weight loss despite a big appetite, which is a different problem worth a visit of its own.
Why does my dog’s fur not grow back after grooming?
Slow regrowth after clipping is one of the classic clues of an underactive thyroid, though coat type and season play a part too. If it has been several months with little change, mention it at your next visit.
Speak to the team at Langley Meadows Animal Hospital
If your dog has slowed down, gained weight and started hugging the heat, phone us to book a check and blood work.
Published by the team at Langley Meadows Animal Hospital.
This article is for general educational purposes only and is not a substitute for an in-person veterinary examination or advice about your individual pet. If you have an urgent concern about your pet, contact Langley Meadows Animal Hospital or your nearest emergency veterinary hospital right away.
Langley Meadows Animal Hospital
#7, 6233 200 St, Langley, BC V2Y 1A2
Phone: (236) 706-0019
Hours: Monday to Friday 8:00 AM to 10:00 PM; Saturday 9:00 AM to 10:00 PM; Sunday 10:00 AM to 10:00 PM; statutory holidays 8:00 AM to 10:00 PM