I second that, I'd put him on his old food until the antibiotics are over and you know where you are with him.
Did you do a gradual change to his new food? Was he eating everything during this gradual change or just picking out the old stuff?
The antibiotics could be causing the upset stomach but it could be the new food or something else. Hope he is feeling better soon.

Once you know what is happening someone maybe able to recommend a good food for older dogs if that if what you are looking for. I feed my dog raw, and that doesn't need to be altered as he gets older, so I have always been oblivious as to why dry foods need to change.

Why don't u put him on rice and booked fish for a few days then quest add boiled fish to his kibble. That what my dog has

Thank you guys so much. It didnt even cross my mind that switching his food and having him on an antibiotic might be too much for him. I think i will keep him on his old food for now.
He has to be on the anitbiotic for a month and the anticipation is killing me, not knowing if my dogs time with me has been cut short. But i have been being positive about it and enjoying my time with him even more.

I did gradually switch his food over over a course of a week. He ate all of it during that week.

Thanks again, i will definitely look into some homemade diets for my dog. That might tempt him more into eating later on when we figure out whats going on with him.

I am unfamiliar with this food. Is this a brand you are getting from your local independent pet store or in a major box/mass store?

Im getting it from Petsmart. I recently learned that it is a Petsmart produced product too.

I've been following this thread with interest as diet is a subject of great interest for both humans and dogs. For both species I believe that food should be geared around 2 things - teeth and ancestry - in other words what are we genetically geared up to eat. For us humans that is an omnivorous diet consisting of nuts, fruit, veg, meat, fish, eggs, a small amount of grains and dogs a primarily carnivorous diet of raw meat, bones and a very small amount of vegetable matter. I hold issue with vets and doctors who stick their oar in with suggesting age-related diets when everything is going smoothly. If there is a case of loss of teeth, then clearly a dog cannot eat a bone or a human chew meat, but why should a dog be subjected to a radical change of diet just because in the space of 24 hours he has now officially become a senior? Every animal including ourselves are individuals and should be treated as such. The advice to put the dog back onto his original food is very sound IMO.

Very well said gnasher. If the dog liked the original food then why change. I have a senior dog but he is still on food that is for a younger dog.

Only thing I'd say in favor of the vets is like us ,our needs change as we get older. When we were eating nuts berries and the like we didn't live to the ages we are now , far from it we were lucky if we made 30. And a wild dog would be lucky to make 10. I'm not saying kibble is all it's cracked up to be anyway . But it's like puppy food u give it because it's got more fat in for a growing dog.il shut up now lol

We were indeed lucky to make it to 30 hundreds of years ago, but this was not due to poor diet unless one was starving but down to lack of hygiene, sanitation, modern medicines and other comforts. Our diets back then were one lucky enough not to be starving was far healthier than today's surfeit of refined carbs. I remain to be convinced that it is a good idea to radically change a dog's diet just because he has suddenly hit double figures. If it ain't broke then don't fix it! Now, if you are talking about a dog who is reaching his senior years and cannot take so much exercise because of, say, arthritis then one might want to cut down on food intake to prevent weight gain, or one may want to moisten kibble because of tooth loss or decay, but other than these simple adaptations as a matter of common sense, I fail to understand why a dog of senior years needs to have his diet radically changed.

Callie is fine with any food. Put it in front of him and he inhales. Sophie is pickier than our cats have ever been. Warm water and tinned food mushed into kibble as a gravy usually works with her.