To entice eating (try 1 at a time!)
1) active play sessions trigger hunt, catch, kill, eat behavior cycles. Try about 15 -20 minutes
2) warm the food to baby bottle temp to get it nice and stinky
3) add some tuna juice from water packed tuna.
4) crumble some crushed dry food over the canned if he is/was a dry food addict
5) FortiFlora - some cats go crazy for this - availaable online or at vet's office
5) a teaspoon of plain yogurt with active cultures may perk interest
6) Cat Sip - milk prepared to reduce lactose. Still has carbohydrate in it, but if it gets him to eat something its worth it
7) KMY - kitten milk replacer - sprinkle a bit of the powder on the food. (You can donate any unused to those fostering kittens if it doesn't work!)
Health Status Checks:
1) smell his breath - do you smell nail polish remover or a fruity smell? If yes, he may be in diabetic ketoacidosis and need to go to a vet ASAP
2) gently pull up the fur at scruff of his neck and release. Does it stay pulled up and only slowly go back to normal or does it snap right back down. If it is slow to return, he may be moderately to severly dehydrated.
3) if the fur snaps back, move on to the gum test. Lift the lip, press your finger on the gums and release. Do the gums pink right back up or do they s l o w l y return back to pink? If the latter, he may be mildly to moderately dehydrated.
4) How has his urination been - oceans, lakes, ponds, cups, or spoonfuls? One or two deposits in 12 hours or multiple?
oceans - ponds, multiple times per day suggest uncontrolled diabetes, renal disease, and hyperthyroidism, to mention a few.
numerous spoonful deposits suggest a urinary tract infection, bladder stones, or interstitial cystitis could be possible. A vet visit with cystocentesis, with a culture and sensitiviy performed may be required. Possibly an x-ray to look for stones.
5) have you tested for urine ketones? Their are instructions in my signature link Secondary Monitoring Tools.
Without insulin, his glucose is likely to begin rising. When in doubt, don't shoot.
After 2 days or more of not eating, hepatic lipidosis may set in, where fat breakdown exceeds the liver's capacity to handle it and causing numerous metabolic derangements. Go to the vet; don't wait until you see him turning yellow from bile backing up into the bloodstream!