About the livestock that was mentioned above: Last year I was in Croatia and Bosnia (not a cruise), and when I came back to the states they asked the same question about whether or not I had been near livestock or a farm. I told them I had, and they asked to see the soles of my shoes. Seems like they are just checking for contaminated soil or animal "waste" that could cause problems for the local animals/plants/people.
Not that it really mattered - I showed him my shoes, which did have some dirt on them, but he didn't question it any further.
RCCL - Adventure OTS (Honeymoon!)
CCL - Carnival Miracle
RCCL - Enchantment OTS