Hi there, this is Dr Linda.
I am sorry that your brother's cat has gone off their food, and udnerstand your concern.
Sharing territory can be incredibly stressful and it could be that she is not coping well with these new arrivals.
However, as the cat is 10, it is also quite possible that there is a medical cause for this appetite loss.
The first step is a vet check, to assess her for e.g.
- Dental disease
- Oral ulcers
- An oral mass
- Chronic kidney or liver disease
- A source of pain such as arthritis
- A viral infection (potentially passed on from the other cats)
The vet will examine her and may also discuss some tests such as a blood test, to determine why she is off her food.
If she is given a clean bill of health, we'd want to work on getting her happier with the other cats.
This can mean things like:
- Ensuring they each have their own space, hiding places and resources.
- Feeding them separately
- Keeping her brain occupied with things like puzzles, games and toys
- Using a calming plug in e.g. Feliway
- Starting her on some calming supplements
Offer her soft food that is easy to eat and temopting such as warm sardines, chicken, egg and.or cat food.
Hopefully this resolves very soon, I know it must be a big worry.