First, I am very glad to hear he isn't likely to have eaten something risky and that he hasn't those other urgent signs I asked about. Still to see grass eating and appetite loss together does suggest nausea. And as I am sure you can appreciate, where dogs just keep eating and vomit, our cats tend to just refuse to eat with this. Of course, we can also see appetite loss with oral pain and breathing issues but that thankfully sounds less likely for your lad.
Anyway, with this suspect nausea afoot, our main concerns here would be a grumbling bacterial infection, viral disease, pancreatitis, IBD, GI cancer, or at his age we can also see this as a side effect of metabolic conditions (ie hyperthyroidism), organ disease (ie liver or kidney troubles).
Now with this all in mind, we can take a few steps here to try to help him. To rule out nausea as an anorexia differential, you can try him on antacid therapy. Pet safe options we can use include Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid), or Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet). Whichever you choose, we’d give this 20 minutes before food to allow absorption. Of course, do double check with your vet if he has a known health issues or is on any medications you haven't mentioned.
As well, you will want to try and see if you can get him eating properly (as I am sure you have been). Favourite foods are allowed or you can tempt with a light/easily digestible diet. Examples of this would be boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used here (ie Hill’s I/D or Royal Canin’s sensitivity.) Though if tempting doesn’t work, then we do have to consider initiating syringe feeds to get a good volume of food in. We'd not have to do this quite yet if he just started with signs but it is a good idea if we see this over a few days since kitties are high risk for liver issues if these situations lingers. In that case, we can offer or syringe feed watered down canned kitten food, Hill's A/D, Royal Canin Recovery, or Clinicare Canine/Feline Liquid Diet. All of these are critical care diets that are calorically dense, so a little goes a long way nutrition-wise. And I'd note OTC cat hairball gel +/- canned pumpkin can be given or added to food to just push any hairballs (or odd items) through the gut.
On top off all of this, you do need to keep an eye on his water intake. Nausea can impact that too, so we do want to check his hydration at this point. To check his hydration and make sure that he isn’t becoming dehydrated, there are a few things we can test at home. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether he has a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this HERE. (http://www.ehow.com/video_12232503_dog-dehydrated.html). They use a big dog but it makes it easier to see and the principles are exactly the same) If you are seeing any signs of dehydration already, then you do want to have your kitty seen by his vet before this gets out of control.
Overall, when a cat is eating and drinking poorly, it can mean a wide range of underlying issues. Therefore, at this stage, we'd want to tread carefully and start the above supportive care. If you do but do not see improvement in 12-24 hours or he worsens (vomits, etc), then you do want to get your vet involved at that stage. They can assess hydration, check for signs of any sinister lumps/bumps or internal issues. As well, you may consider having them check a blood sample to assess the state of his organs. They can also cover him with antibiotics, anti-nausea/vomiting medication by injection and even appetite stimulating drugs if necessary. Depending on the findings, the vet will be able advise you on what is likely our culprit and what can be done to help your wee one before he just fades away on us.
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