In modern times, livestock is regularly shipped en masse from places with surplus arable land, like Australia, to places with a dearth of arable land, like Saudi Arabia, although I don't know what happens to the animal waste.
I think the animal waste is washed into the sea. Presumably there are sumps on the deck and someone hoses the deck (and animals!) with seawater.
> Using the table below, and assuming one million head of cattle a year, 20 kilograms (44 pounds) of excrement per head per day, an average voyage time of 10 days and vessel loading and unloading times of five days, something in the order of 300,000 tons of excrement is pumped into the sea during these voyages each year. A similar calculation for sheep, voyaging more typically for 20 days, would add a further 85,000 tons.
> The excrement has a high water content and is considered benign. It is treated like sewage under Marpol Annex IV and doesn’t need to be treated before dumping far from shore.
> Using the table below, and assuming one million head of cattle a year, 20 kilograms (44 pounds) of excrement per head per day, an average voyage time of 10 days and vessel loading and unloading times of five days, something in the order of 300,000 tons of excrement is pumped into the sea during these voyages each year. A similar calculation for sheep, voyaging more typically for 20 days, would add a further 85,000 tons.
> The excrement has a high water content and is considered benign. It is treated like sewage under Marpol Annex IV and doesn’t need to be treated before dumping far from shore.
https://maritime-executive.com/features/live-export-followin...