Low-phosphorus food for Leonberger puppy

A vet-flagged phosphorus concern in a Leonberger family line is something worth taking seriously from day one — the good news is that at 9 months you're catching this at exactly the right time to make a real difference. Puppy nutrition is honestly one of the most important investments you'll make; the right food in the first year sets the foundation for everything that follows, and the differences between puppy foods are more significant than most people realise. To point you to exactly the right option — what's your Leonberger currently eating, and did your vet give any specific phosphorus thresholds or just a general steer to keep it low?

That's really helpful context. Royal Canin Giant Junior is a solid giant-breed puppy food in most respects — controlled calcium and phosphorus for bone development — but you're right that it's not specifically formulated with kidney protection in mind, it's just managing skeletal growth. For Marta, given the bilateral family history, I'd want something that actively keeps phosphorus on the lower end while still supporting a giant breed puppy who has significant growing left to do at 9 months. Can I ask — is your vet open to a prescription diet, or are they looking for something available over the counter? That changes which route makes most sense.

Perfect — that actually makes things clearer. In that case my recommendation is Hill's Science Plan Large Breed Puppy with Chicken. Here's why it's the right fit for Marta specifically: Hill's has published phosphorus content of around 0.36% on a dry matter basis for this formula, which is meaningfully lower than most giant-breed puppy foods including Royal Canin Giant Junior. It's still nutritionally complete for large and giant breed puppies — controlled calcium-to-phosphorus ratio to protect developing joints, appropriate calorie density so she doesn't grow too fast, and high-quality protein for muscle development. It's not a renal diet, so it won't under-support her growth, but it takes phosphorus load off the kidneys in exactly the precautionary way your vet is describing. It's also widely available on Amazon UK and straightforward to transition onto from her current food. I'd do a 10-day gradual switch — she'll likely take to it well. One thing to flag: at around 12 months you'll want to revisit, because Leonbergers are often kept on puppy food until 18–24 months given how long they take to mature, and you'll want to confirm the adult transition timing with your vet given her history.

Yes, absolutely let your vet know — not because it requires approval, but because if they're keeping an eye on Marta's kidney markers over time, knowing what she's eating gives them a useful baseline. During the transition itself, watch for loose stools in the first week, which is normal as her gut adjusts; if it persists beyond day 10 or becomes watery, slow the transition down rather than pushing through. With Leonbergers specifically, also keep an eye on her coat — giant breeds can occasionally react to a protein source change, so if you see any skin flare-up note it and mention it at her next check. But Hill's Large Breed Puppy is a very well-tolerated formula; most dogs transition onto it without any issues at all. You're doing exactly the right thing being proactive about this.

That's the perfect plan. Hill's Science Plan Large Breed Puppy with Chicken — available on Amazon UK in 2.5kg, 12kg, and 18kg bags, so worth going for the larger size once you know Marta's happy on it. Good luck with her, and enjoy this stage — 9 months in a Leonberger is a wonderful, chaotic time!