I wish we had a heads up before all of this had happened. I would have made my chickens and piggy younger so I could have taken them with me. R.I.P. Hambone and my chickens: nugget, cordon bleu, and crispy.
I do believe that any animals you had in your old/new house were turned into eggs. These eggs can be instantly hatched with an interactive menu when you click on them. The box you will find them in is the area they were in ie: old house box, back yard box etc. They are not gone, just reversed to eggs. You will have to rename them I do believe.
edited to add: I'm a bit slower...I blame the flu.
I had the same three chickens the entire time I lived in my house. I feel kinda bad for not youthifying all my animals before the change, but since they turned into eggs, it's like they're the same chickens, reincarnated.