Feral cats

I have a couple of feral cats that come and go as they please. When we can
get hold of them we take them to the vet and have them spayed and get them
shots, etc. We feed them a mix of good quality can and dry cat food. We
would like them to stay around since they keep the mice down. We live on a
farm.

Anyway, this morning one of cats returned after being gone for three days.
It ate several times during the day and then laid in the sun. This evening
it ate a little more and then wanted attention. It was then I noticed that
it's abdomen was extremely rigid. He would let me pet his stomach and there
didn't seem to be any discomfort. I'm wondering if the cat has simply
stuffed itself causing the rigid stomach or could this be a sign of worms or
some other parasite? I've never had a cat that exhibited this regardless of
how much it ate. All the others quit eating when they are full. Will a cat
stuff itself if meals are few and far between?

Thanks for any info
DFB