Michelle, what other things have been tried for Freddy before? what investigations have been done? As MM mentioned, urine tests etc? What about diet, have you tried changing that? Have you tried Cystaid or Zylkene?Cystitis very often can be stress related, but as you said, stress to a cat could be something as simple as another cat sitting where he wants to sit, or another cat looking at him the wrong way - subtle things that we wouldnt think as being stressful. More often though, its a combination of stress, diet, water intake, weight, activity levels etc.
I know with my Ben when he had cystitis years ago, and ultimiately a blockage, to me at the time, he didnt seem stressed. But when I really sat and thought, there were stresses in his life at the time it started, made worse by moving house, plus I was feeding dry food only. It tipped him over the edge, once I researched it, changed his diet and things settled after the move - he never had another problem.
