Dog food allergies & hypothyroidism in Spaniels

A Springer with hypothyroidism and ongoing GI upset after meals — that's a combination that needs a bit of careful unpicking. True food allergies in dogs are actually less common than food intolerances, and the two can look identical from the outside. The thyroid condition adds a layer of complexity, because hypothyroidism can itself slow gut motility and make digestion less efficient, which sometimes gets mistaken for a food reaction. The most reliable way to separate what's diet-driven from what's thyroid-driven is a proper elimination diet using a novel or hydrolysed protein source. To give you useful advice: is your Springer currently on medication for the hypothyroidism, and what symptoms are you seeing after meals — vomiting, loose stools, excessive gas, or a mix? Has your vet weighed in on the diet side of things, or have you already tried switching foods?

That's really helpful. Stable thyroid levels on levothyroxine is good news — it means what you're seeing now is unlikely to be thyroid-related and is more probably a genuine dietary intolerance. Mucus in the stool in particular points toward gut inflammation, and chicken is actually one of the most common protein intolerances in dogs, especially those who've eaten it their whole lives. The gut can develop a sensitivity to a protein it's been exposed to repeatedly over years. Given that, I'd move away from chicken entirely and look for a food with a protein source she's never had before — that's the basis of an elimination diet. I'd also avoid grains for now, since some dogs with sensitive guts do better without them, though they're less often the primary culprit than the protein.

For a 6-year-old Springer with this profile, I'd recommend Forthglade Complete Grain Free Adult Dog Food with Turkey — the wet food trays rather than kibble. Turkey is a novel protein for most chicken-fed dogs, it's a single clearly-labelled meat source, and Forthglade's ingredient list is genuinely clean: turkey, sweet potato, and vegetables, with nothing hidden. The wet format also helps because it's easier to digest than dry kibble, which matters when the gut is already inflamed. The lower carbohydrate load compared to most dry foods is a bonus too. Importantly, it doesn't interact with levothyroxine — some foods high in calcium or soy can affect thyroid medication absorption, but Forthglade Turkey is fine on that front. Transition slowly over 10 to 14 days, keep everything else constant, and give it a full 8 weeks before judging — gut inflammation takes time to settle. If symptoms resolve, you'll have your answer.

It's a sensible thing to check. Levothyroxine is best given on an empty stomach — ideally 30 to 60 minutes before a meal — because food can reduce its absorption. High-calcium ingredients (like cottage cheese or some supplements) and soy can specifically interfere with the medication if given at the same time. Forthglade Turkey doesn't contain either of those, so it's fine to feed after you've given the medication and waited the recommended gap. If your vet hasn't mentioned the timing protocol, it's worth a quick call to confirm the gap they want you to leave — some vets are specific about it. But the food itself isn't a concern.

Good plan. One practical tip: keep a simple diary for the 8 weeks — just a line a day noting stool consistency and any gas or discomfort. It sounds tedious but it's genuinely useful, especially if you want to go back to your vet with something concrete. If things don't improve after 8 weeks of strict elimination, it's worth asking your vet for a referral to a veterinary gastroenterologist or requesting a hydrolysed protein food on prescription, which breaks the protein down so small the immune system can't react to it. But Forthglade Turkey is a solid first step and works well for a lot of sensitive dogs.