Senior guinea pig losing weight? Nutrition help

Gradual weight loss in a five-year-old guinea pig is something worth taking seriously — at that age they're firmly in senior territory, and dropping condition slowly is one of the earliest signs that their nutritional needs have shifted. Before I point you toward anything specific, can you tell me a bit more? Is your Rex still eating normally in terms of appetite and interest in food, or has that dipped too? And is he kept with a companion? Knowing whether this is purely a nutrition question or whether there might be something else going on — dental issues, for instance — will help me give you the most useful steer.

That's really useful context — and honestly a good position to be in. If the vet has ruled out dental problems and underlying illness, diet is exactly the right place to focus. Senior guinea pigs often struggle to extract enough nutrition from standard adult pellets, and their ability to maintain muscle mass and body condition declines even when appetite stays strong. The key things to look for in a senior-appropriate feed are higher quality protein sources, added vitamin C (guinea pigs can't synthesise their own and older animals are more vulnerable to deficiency), and a formulation that's easy to digest. Can I ask what he's currently eating day to day — pellets, hay, fresh veg? That'll help me make sure any recommendation genuinely fills a gap rather than just swapping like for like.

That is a solid baseline — Timothy hay and leafy greens are exactly right, and you're already covering vitamin C deliberately which puts you ahead of most. The gap I'd look at is the pellet. Science Selective Adult is a good food, but at five years old your Rex would benefit from a formulation with a slightly higher crude protein level and added joint and digestive support. My recommendation is Burgess Excel Guinea Pig Nuggets with Blackcurrant and Oregano — specifically the version marketed for all life stages, but more importantly I'd switch him onto Supreme Science Selective Senior Guinea Pig. It's formulated with increased protein, prebiotics for gut health, and a softer texture that older guinea pigs find easier to process even when their teeth are technically fine. It's widely available on Amazon UK, comes in a 1.5kg bag, and the gradual transition over a couple of weeks means you won't upset his digestion. Keep everything else the same — the hay, the veg, the pepper — and give it six to eight weeks before judging whether his condition is stabilising.

Good question — portion size matters more than people realise with pellets. The general guidance for guinea pigs is around 30g of nuggets per day per animal, and that applies to the Senior formula too. The key thing is that pellets should always be the smallest part of the diet by volume — unlimited hay is the foundation, and that doesn't change with age. If anything, as guinea pigs get older and gut motility slows, hay becomes even more critical. So 30g of the Senior nuggets daily, unlimited Timothy hay, and the fresh veg routine you already have is a well-balanced senior diet. Weigh him weekly if you can — a kitchen scale works fine — so you have a clear picture of whether the trajectory is improving, staying flat, or continuing to drop. If he's still losing after eight weeks on the new food, that's the point to go back to your vet for bloodwork.

Completely understandable concern — separate feeding is a bit of a faff but in this case it's worth it if you can manage it. The Senior formula has a higher protein level that's appropriate for an older animal but slightly over what a healthy two-year-old needs long term. The practical approach most owners use is to feed them in separate spaces for the pellet portion of the meal — just ten minutes apart, or in separate rooms if needed — then return them together for the rest of the day. The hay and fresh veg can obviously be shared freely. It's not the end of the world if the younger one occasionally eats some Senior nuggets, but as a daily diet for a two-year-old, sticking to the adult formula is better. The extra effort is genuinely worth it given what you're trying to achieve for your Rex.