I find that cats like the smell of *fresh* food. So try and seal the food
well.
It's easy to get cat eat the old food: Put it in a bowl and sprinkle some of
the fresh stuff over it or mix it in.
That's how I get rid of the stuff I bought but that isn't appreciated that
much.

Carola

You could try to trick him by mixing a little at a time into the new food.
Or just donate the old bag to the Humane Society or to someone who feeds
ferals.

Sherry

An update on my 19 year old cat.  He is now on his way
to Rainbow bridge.  

The vet examined the cat, even though he had diarrehea
he had an area of "constipation" that was still present.
The only real option was to sedate the cat and
attempt to drain the constipation.  

We decided to put the cat to sleep, it turned out
to be a wise decision because the cat never would
have survived the sedation.   The sedation the
vet gave him was enough to end it.  

Also the cat weighed 5 pounds now, he was 15 pounds
sevral years ago.