After spending a week anchored offshore, the Bader III docked on Friday morning and began loading cattle in the afternoon.

Sheep were expected to follow ahead of the ship's departure as early as the weekend.

But Greens Senator Sarah Hanson-Young said the vessel had a terrible record for animal deaths and the government should stop it from leaving port.

"This ship has the highest recorded number of sheep deaths," she told reporters on Friday.

"It is a ship of death."

The RSPCA backed the senator's calls, with animal welfare advocate Rebekah Eyers describing the Bader III as one of the worst live export ships because of its two-tier deck design.

Dr Eyers said that exacerbated ventilation problems and made welfare checks difficult.

"Given all the evidence we have about animal suffering on these long-haul journeys, it is just not acceptable for the federal government regulator to allow this ship to load without any improvements to on-board conditions," she said.

Animals rights groups planned to protest at Port Adelaide on Saturday, but brought that forward to Friday night after loading began.

The Adelaide Against Live Export group said the sheep due to be loaded were currently being kept at a feedlot north of the city.

Their action came after the ship which sparked the current row over live exports prepared to leave Fremantle for northern WA to pick up cattle bound for South East Asia.

The Awassi Express was held up for about three weeks after Australian authorities forced it to make improvements to its ventilation system following the deaths of thousands of sheep to the Middle East.

Australian Associated Press