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We don't become concerned about a cat not eating until they reach the third day, at which point there is an increased risk of hepatic lipidosis. During this time, it won't hurt to offer him different types of food such as an egg scrambled without any additives, slices of boiled chicken breast and so forth. If vomiting, diarrhea or other symptoms begin during this time, the concern for an underlying cause is increased and it's recommended for Milo to see a vet promptly.
At 8 years of age, this could be anything from an upset stomach or lack of interest in his food to dental issues, hyperthyroidism, diabetes, etc. Without additional symptoms, I wouldn't worry just yet. Do spend time this evening and tomorrow enticing him to eat. If this does not happen, I would recommend pursuing diagnostic treatment at your vet's office or ER on Saturday to determine if there is something hindering his appetite. You certainly don't want to rush to the vet if it's not needed, but also don't want to wait too long where liver issues could set in.
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