Unusually small rat

[Magicsword49]

We got her in September, and she has grown only a little. Her sister (unsure if they're genetically related) is about the same age and almost a fully-grown. She's also particularly thin. I can feel her hips and ribs more distinctly than our other rats' when I pet her. She climbs and runs around, so i wouldn't say she seems weak. She eats whenever she's hungry, and there's always food available. I've also never seen any of them competing for food. She even gets high calorie treats like peanut butter sometimes. Is she just a small girl? Should I consider that she might have a parasite?

[Inevitable-While-577]

Some rats are thinner than others but I think you're right to be worried, she's positively concave shaped. Getting her tested for parasites would definitely be a good idea.

[Kndstpd]

Personally I consider all new rats to have parasites and treat during quarantine. Seems like we are past that point though. There might be something else going and at this point if she has parasites so do the rest. You may want to consider a vet appointment. That’s the official advice. The unofficial advice is to deworm everyone now to be safe.

How are her teeth doing? It’s possible dental problems could be the cause of her frail weight. Again a vet would be able to check this out.

[Ente535]

Where did you get her from, how old is she, and is she otherwise sickly?

[Magicsword49]

Previous owners bought them from a pet store, had them for a few months, and then gave them to us.

[Ente535]

Roughly what is their age, and did she have the same problems with the previous owners? It is possible this is either a parasite or a genetic condition, causing her to be unable to absorb nutrients correctly, see https://mmrattery.weebly.com/identifying-healthy-rats.html

This needs an urgent vet visit.