Aniamls on Edge... Any fix?

So were having an odd issue where after a few weeks all the animals end up on the edge of the world. basically as we kill them, they don't seem to respawn anywhere but the edge... Is there any plugin or anyway to help force animals to spawn everywhere..

Odd issue =)

 

How long have worlds had edges? I thought it was infinite o.o

 

We have a border set.

its really odd cause we've had our map about 5 months now, and literally I can go around for 10 minutes and I wont find a single animal. If I go to our borders, there are hundreds. Its like after they die they have a chance to respawn anywhere, over time they built up on the edges...

EDIT by Moderator: merged posts, please use the edit button instead of double posting.