Nice looking pig and chickens.
Now, some may disagree with me, but I think you will be ok with the galvanized. It's not ideal, but I don't think you will be getting temperatures high enough to start melting the zinc coating off of the steel. I work in a steel company where we make galvanized steel and we are around a giant vessel of molten zinc. The temperature is high enough that the zinc is molten but not high enough for the zinc to start gassing. For that you would need temperatures of 1665F. Even for the zinc to start to melt temp would have to be 787F.