For nearly 4 months now, my best friend and I have been breeding mice. We keep our males in cages on their own, with plenty to do.
One of the first mice we got was a tri colored male, who we named Forrest. Predominantly fawn, he has large white patches with black splashes all over.
He has NEVER been a fat mouse, large yes, but not fat. Though in the past few weeks, he's gone to being disgustingly fat. Strangely though, he doesn't eat all that much and he is constantly running on the wheel. It seems he gets fatter and lumpier every day. He's always been fairly slim though, for a large mouse, due to running on the wheel all the time.
Today, I was holding him in my hand, and my friend gently pressed against the sides of his belly to see how fat he really is, and he squeaked when she did so, then urinated all over my hand.
He has never peed on any of us before, so we think maybe its possible he might be in pain?
Could his large size be a tumour of some kind perhaps? I've read that mice can get tumours.
In these pix, you can't tell exactly how fat he is, but he really is fat!!!