Cat has brought in a baby rat or mouse

Question
Last night I interrupted my cat holding with what I thought was a mouse. As usual, mouse seemed unharmed but it was in shock. I have a mouse cage in which I put such mice until the next day when, if okay, I take to a local hedgerow and release. This morning the mouse looked dead but it wasn't.  It was rigid and cold but moved when I touched it. I held it in my hands for half an hour and life began to stir. It was making strange movements with its mouth and I thought it was dying, gasping for air. Eventually it began to right itself and sit although in a very sluggish way. Its eyes were wide open though closed a little while warming up. When it seemed warm and more relaxes, I placed some water under its nose. It seemed to half lick. I tried different food and it did seem to sniff it and possibly licked apple (the whiskers responded) but it pulled its nose away. On looking at the "mouse" I'm having my doubts that it's actually a mouse. I'm beginning to think it's a rat. It's head is bigger than other mice I've rescued, it's paws also seem bigger, even though it's very small itself. Its fur also seems softer and thicker than other mice I've rescued. If it's a rat, what do I feed it if it's only just weaning from its mother? I've read that soya milk can be fed to a pregnant mum, or scrambled egg. Will this fully furred, eyes open, possible baby rat be okay with this? If it survives, when should it be released so that it will survive?

Answer
It may had been in shock and that could have been why it was so slow to start going.
I doubt it is not weaned from the mother if it is as old and large it is, you can try some kitten formula if you cant find any rat formula at the local pet store. I would release it once it is moving fine and eating fine.