[Kajazy]

I've been accumulating a mass of soiled guinea pig hay (including their poo etc of course!), and wondered whether I could use it straight as a mulch in the summer...?

[Trillium]

Even though the guinea pig is vegetarian and doesn't have the same pathogens in its poop, you still need to compost the manure first. Same with other vegetarian livestock.

I have put 'fresh' rabbit poo around my roses on occasion with no ill effects but it did not contain any pee, which can contain ammonias that plants don't tolerate well, in the straw.

[bazh]

Just store what you've collected already under some form of cover and it'll be fine come the summer when your looking at using it.

If you have a compost heap I'd probably just add it the rest you to that though as part of your browns (Carbon rich) element. Just watch out for any leftover feed mixed in with it, it may attract other rodents less welcome.