This may not be an issue as much as my own stupid fault. I accidentally played my world without the mod loaded. Once I realised I restarted the game with the mod but I had lost the kangaroos I had tamed and also the surrounding area where I was has lost all the mobs from the mod apart from the odd fly. The mobs still spawn in other areas but I have to travel a few chunks away before encountering them. Is there anyway of restoring the tamed mobs I lost or at least making new mobs spawn in this area? And no, stupidly I don't have a backup :(

It is your own fault as that happens when you load a world that uses mods without the proper mods installed.

you'd have to spawn those mobs back in btw

Thought as much. Oh well - thanks for the reply :)