When you've got an older dog, things change. My own Lettie got to the point where she simply stopped eating the same food she lived 10 years on and we had to change. She was diagnosed with Chronic Renal Failure, which you can only treat in dogs with lots of changes to their diet.
Mainly, you need to reduce the amount of protein, phosphorous, and potassium in their food as well as increasing the water.
There are special diets but dogs generally hate those.
So what do you do?
I've switched from regular dog food to a combination of "Lettie's Burgers" and treats. The burgers have added bread crumbs in them to reduce the protein, and the treats are all low protein treats of 12% protein or less. Normal Dog Food is around 26%, 70% Lean Ground Beef when cooked is about 18%.
The problem is that those treats are expensive and probably not the best for your dog. The solution is an interesting one.
Those same cans of Renal Diet food that she hates when scooped out into a bowl can be made into a treat, as well as any wet dog food with a paste consistency.
Simply slice thin, about the thickness of a tortilla chip but under 1/4 of an inch, and bake in the oven. 350F for 30 to 45 minutes depending on thickness until crispy. Store the resulting Dog Food Jerky in the refrigerator and use within a week.
That of course depends on whether your dog likes chewy or crispy treats. My own experience last night was that 40 minutes at 1/4 inch thickness gave a chewy treat. 1/4 inch is about 1/2 the width of your smallest fingernail, your pinky - very roughly.
The proof was in the pudding though, the very thinnest crispy pieces that were like a potato chip, Lettie devoured. The thicker ones were like a Jerky that she ate slower, and the thickest ones she wouldn't consider eating.
That's my own dog, your dog will have their own preferences. I'm sure if you have an older dog you know them by now.
This morning, I had a pickle jar full of little roughly triangular pieces of Dog Food Jerky and she ate about 1/3 of it so I call this recipe a success. The one can made a "full" pickle jar.
If you have dry dog food that you can't get your dog to eat, try pulverizing it in a blender and then adding back water until you get this same paste consistency. Then you can always try feeding it directly or baking it until done.
Again, remember that thin is best!