By way of an update to those of you who were kind enough to give me your ideas it seems that the cause of our cat's problems has become clear.
One morning last week I noticed that our female cat, Millie, seemed very uncomfortable and was unsuccessfully attempting to spray around the room. She was making herself very obvious which is very unusual for her. I took her to the vet as soon as I could that morning as I thought that her recurrent cystitis had returned with a vengance, causing her difficulty to pass urine.
The vet felt Millie's bladder and said it was solid and she could not express any urine so asked to keep Millie in for a urine test and, depending on the results, a scan of her bladder. The results showed terrible cystitis and a secondary infection, so she then did a scan. Unfortunately the scan showed a tumour totally filling Millie's bladder which was apparently extremely fast growing and our only decision was whether she should be put to sleep straight away (while still under anaesthetic) or whether she was brought round so we could say goodbye. I could not believe it - that morning I first noticed a problem and by lunchtime we had had to have the poor girl put to sleep. It was terrible shock for us.
Rosco has not had his pooing problem since that day and has successfully been using the litter tray, so I think that poor Rosco had sensed that something was wrong with his sister and was doing his best to tell us.
