No worries. I appreciate that most people don't' check their cat's gums on a regular basis.
That aside, I would suggest having a word with the person who fed him to see if he did eat properly while you were away. As well, do double check that they didn't see diarrhea in the litter box while they were cat sitting him.
Now Fringe does sound to be a stressy cat and based on his history I would be concerned that there is more to what we are seeing here. First, since stress has an immune dampening effect, we have to be wary that he currently has a brewing GI infection playing a role here too. This is especially suspect since lip licking is a nausea sign in cats and the selective grazing of food is another. As well, if there is any chance that he didn’t eat properly while you were away (which I very much suspect with the weight loss) then there is real risk of fatty liver syndrome from this and that often causes nausea and appetite loss as well for cats. And it can make it more of a challenge to get them eating again.
With this in mind, we need to tread with care here. If he eat wet food for us,t hen I would suggest using a calorie rich diet (ie Hills A/D, Royal Canin Recovery diet, even canned kitten food) or a liquid diet (ie Clinicare, Catsure) with him. As well, there are paste supplements (ie Nutrical) that can also be used. Each of these has more nutrition per bite even if we cannot get much in and will help get more weight back onto him sooner. (And if the weakness in the back legs is due to muscle loss from self-starvation, then getting nutrients in will help with that too.
Of course, if that appetite wanes any more or he has any vomiting, then we'd want to have a check with his local vet. They can check for infection and rule out fatty liver syndrome by checking a blood sample. Depending on their findings, he may just need an injection of an anti-nausea medication, antibiotics +/- appetite stimulants. Of course, if they find severe signs of this complication, then IV fluids may also need to be considered.
Finally, since he is a cat that stresses with life changes (be it a new house or you away), I would note that he could benefit from a de-stressing support for future changes that could upset him. Often we will use Feliway, (also known as Comfort Zone in the pet stores) which is a synthetic cat pheromone that helps to relieve stress. This can be used as a spray or a plug-in diffuser. There is also a diet on the market called Calm by Royal Canin that contains a number of stress relieving supplements. As well, there are nutritional supplements like Zylkene and Kalmaid to soothe anxious cats that could also be used here to help him cope at those times. And as they are not drugs per say, they can be used together as needed. Furthermore, he may benefit from a cat sitter he knows staying with him or even being boarded by his vet.
Overall, Fringe's situation doe sound to have its roots in being stressed while you were away. Still, because of that we are now facing a few potential issues for him. So, we do want to increase his calorie intake with the above. But if he doesn't start perking up or if we see any other nausea signs (ie gagging, retching, further appetite loss), then we'd need to plan to have a check up with his vet to address those other issues so we can nip them in the bud for him.
All the best,
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