My understanding is that lime is used to increase the ph of soil. Most plants like a slightly acid soil but if there is lots of manure it gets TOO acid, so lime, being an alkali, helps redress the balance. My favourite toy last year was y pH meter!
I've also read that liming soil where chooks have been also helps to get rid of parasites such as worms.
Normally, soil would be limed once a year, I think, is spring. I'd try and keep livestock off until it's washed in.