Siba Ships is considered the world's leading maritime livestock transporting company.

The vessels will be built at the Uljanik shipyard in Croatia, which built the flagship of Siba Ships' livestock fleet, the MV Becrux in 2002.

According to Wellard Rural Exports, the new vessels will each carry 17,000 cattle or 75,000 sheep in comfort and security.

The vessels will enter service in 2011.

Siba Ships' investment in the new vessels is in addition to its previously announced $US80m investment in two smaller livestock carriers, the first of which is due to be launched in late 2008 or early 2009.

Siba Ships Chairman Mauro Balzarini said the MV Becrux was the world's first new construction large livestock carrier, and set the benchmark for animal welfare standards.

"After almost 80 successful voyages we now know that we can deliver livestock to their destinations happier, healthier and heavier than when they boarded," he said.

The two new ships will boast a similar design to the MV Becrux, with the addition of modifications to improve operating efficiency and animal welfare.

"That benefits the animals, the producers, the shippers and the receivers, and we see significant and increasing demand for this standard of livestock carriage, which exceeds governmental standards and is totally focussed on animal welfare," Mr Balzarini said.

"Using these vessels we know that the animals will arrive in better condition than when they boarded, which makes both welfare and commercial good sense."

The new vessels will be 180 metres long, nine decks high and will boast stronger ventilation and better air and fodder distribution systems, higher redundancy in livestock services and will be more environmentally friendly.