I wonder if you can help?!

I have a female Whooper Swan with a severe limp, its her left leg.

She has been to the vets, had x-rays, scans all sorts of things and we've been told there isn't anything physically wrong with her leg. She is now showing new symptoms - weak 'S' shape lent on her back when she is sitting, loss of appetite and very lethargic.

We were under the impression it maybe some sort of poisoning but we have 3 baby black swans with her, another baby Whooper and a family of mutes.

I hope you can help!

Thank you very much

Hannah