Before upgrade I had a passive chicken farm for feathers.

It ran marvelous, after upgrade and two Minecraft days all my chickens where gone.

Luckely I saved up aload of Eggs so I spawned around 20 chickens, fed them till  around 40.

2 or 3 minecraft days later... all gone, so maybe the Ocelots got hungry. Build a 2 block think and 2 block high wall with double doors, Spawned again chickens... gone. If you need anything please ask I will do my best to create as much information as you need,