Health & Medical

I spent most of a year convinced I was overfeeding my dog. Cut the kibble by a fifth. Then a third. Swapped to a light formula, cut the treats, added an extra walk. He kept gaining, and he kept getting slower, and by the following spring he was sleeping fourteen hours a day and his coat had gone thin along both flanks.

It was his thyroid. It had been his thyroid the whole time.

Hypothyroidism is the thyroid gland not producing enough hormone, and since thyroid hormone sets the speed of the whole metabolism, a dog running short of it slows down in every direction at once. It is common in dogs, unlike cats, who get the opposite problem. Middle-aged, medium to large breeds most often. Golden retrievers, dobermans, boxers, setters, and a long list of others carry more of it than average.

The reason it goes unrecognised for months is that every individual sign looks like something else.

Weight gain without eating more. That gets blamed on food, as I did. Lethargy and reduced tolerance for exercise gets blamed on age, especially in a dog of seven or eight where slowing down seems reasonable. Hair thinning, usually symmetrical on the flanks and tail, gets blamed on season. A dull, dry coat, and skin that turns greasy or flaky and picks up recurrent infections. Some dogs get dark pigment patches on the skin. Many seek out warm places and feel cold to the touch, which was the one that eventually made me suspicious, because he had started lying on the radiator pipe in June.

The stranger signs

A few presentations do not look metabolic at all. Some hypothyroid dogs develop a drooping face, one side or both, from nerve involvement, and it reads as a stroke. Some get a head tilt or a lack of coordination. Behaviour changes happen too, most often a dog who seems dull or withdrawn, though aggression is occasionally reported. Fertility problems in breeding dogs are another route to diagnosis.

Blood testing is how it is confirmed, and there is a trap here worth knowing about. A basic total T4 can come back low in dogs who are not hypothyroid at all, because other illnesses suppress it, and certain drugs including steroids and some anti-epileptics do the same. That is called non-thyroidal illness and it produces a lot of misdiagnosis. A proper workup usually pairs T4 with TSH, and sometimes free T4 by a more specific method, and it is read alongside the clinical picture rather than in isolation.

So if your dog has been diagnosed on a single low T4 with no matching symptoms, that is worth a conversation. And if the symptoms fit but the first test was borderline, retesting a few weeks later once anything else is resolved is reasonable.

Treatment is where this stops being a depressing story. It is a tablet, levothyroxine, once or twice a day for life, and it is inexpensive. Not a special diet, not surgery, not a specialist. A tablet.

The response is dramatic enough that owners often describe getting a younger dog back. Energy returns within a couple of weeks. Weight starts moving in the second month. The coat is slowest, taking three to six months to properly regrow, and it sometimes comes back a slightly different texture. Mine took until August, and I remember noticing the flanks had filled in while he was rolling in grass.

Dosing needs checking. A blood test roughly four to six weeks after starting, timed relative to the tablet, because the level in the blood peaks and troughs and the timing of the sample changes what the number means. Ask what time to give the tablet on test day, since guessing invalidates the result. After that, once or twice a year for life, plus a recheck any time symptoms drift back.

Overdosing produces the reverse picture: restlessness, panting, drinking a lot, weight loss. Uncommon but worth knowing, and it resolves with a dose reduction.

Give the tablet consistently and away from food where possible, as calcium and certain foods reduce absorption. An hour before a meal is the usual advice, and if that is impossible in your household then being consistently inconsistent is better than random, because the dose is titrated to whatever you actually do.

He lived another five years after that diagnosis and I still think about the year I spent slowly starving a dog whose problem was a gland. If you have a middle-aged dog who is gaining weight on less food, slowing down, feeling the cold, and losing coat, ask for the blood test specifically. It is not expensive and the answer arrives in a couple of days.

The vet who found it did so in about four minutes, having watched him walk across the consulting room and then put a hand on his chest and said he felt cold for a dog in a warm room.