Idea from fiery
A block that is a unloading gate for animals to remove them from the truck.

Expanding on this idea
A loading & unloading block for the following things.

items
Mobs( passive only?)
Liquids

back up to the loading doc and will load the trucks inventory ( with mobs items liquids etc)
back up to the unloading doc and it will remove from the inventory and spawn mobs or store the items in a chest.

If we add liquids then we need a different trailers to put on the back of the semi.
one for a tanker one for animals and one for items