Liz Buchanan BVSc MRCVS
Hello! There was a time when old vets might have told you that the occasional bout of vomiting can be normal, but as we have learned more about cats, vomiting is largely considered a sign of pathology. It sounds as though this may be too frequent to ignore as 'one if those things' and must be difficult to contend with at home. Beyond taking simple measures like worming them with a proper veterinary wormer (no point using a cheap one that may or may not kill the worms, as it leaves you no further on - speak to the nurse), your cats really need to see a vet to get this diagnosed. I can see that you have tried a lot to rule out dietary causes, and some of these - such as trying to slow the eating down - are good practice in any case. This leaves me with three possibilities: 1) that you are not trying these foods for long enough for the cat to have time to adjust 2) that you are swapping one poor food for another (I don't know the foods you mention and have not researched them) or 3) - and quite possibly - it is simply not a dietary issue, or else it's a dietary issue that is complex than that. Pancreatitis is a biggy that can sometimes fall into that category. Stress may be implicated. However liver disease, kidney disease, diabetes, cancers, hyperthyroidism, may also all be on the list.
You say that you can take one cat for testing - that would only be useful if all three cats had the same issue. However, they are different ages and so on, so this may not be the case - we would advise getting all three checked. It probably sounds obvious, but there is no magic test or blood test that flashes up the answer as to what is wrong with a cat - often diagnosis is a process of eliminating the most likely thing (and tests are one tool to help with this). It helps to think through the history for each individual cat beforehand - for each separate cat, when did you first notice them vomitting? How often are they doing it? Where and when are they doing it? How old (you've told me this)? Do they hunt? How are they in themselves? How much is each cat drinking, roughly? When were they wormed / what with? What are their activity levels? Having this written out for each cat can save valuable consulting time (therefore money) and may give your vet some early clues as to what's going on / which cat most needs your resources. Always ask about money from the outset and never be ashamed about it - this way your vet can spend what money there is in the most helpful way.
Reducing stressors in the household, such as ensuring that each cat has their own separate territory / place to hide and can get away from you and the others, costs nothing but please don't waste time on this - if one of them has diabetes or kidney disease for example, they may need your help now.
Best of luck and please let me know how you get on.