The U.S. Department of Agriculture is investigating the death of 13 pigs last summer en route to Hawaii from Oakland, Calif., on Matson cargo ships.

The probe is in response to a complaint filed by the People for the Ethical Treatment of Animals. In a letter to the national animal rights group yesterday, USDA officials said their investigation could take up to two months.

On the June 20-25 voyage of the Matson Navigation Co. cargo ship Mokihana V-128, six pigs died and were disposed of at sea, PETA said a news release from its headquarters in Norfolk, Va. There were 549 pigs on the vessel, including 93 headed for Schofield Barracks, according to the shipmaster's declaration.

During the July 11-16 voyage of the Matson ship Mahimahi V-154, seven pigs died. There were 623 pigs, including 95 pigs ordered by the Army, in that shipment, according to PETA.

Some of the animals were for human consumption, while others were headed for Schofield Barracks to be part of an Army medical training exercise for soldiers preparing to deploy to Iraq.

PETA said it learned of the animals' deaths through pig import permits and the shipmaster's declaration documents filed with the state Department of Agriculture.

PETA's three-page complaint asked the USDA to determine whether there were any violations of the U.S. Animal Welfare Act involving pigs destined for Schofield Barracks.

Jeff Hull, a Matson spokesman in Oakland, said he could not comment on the complaint since his office has not seen it.

Schofield Barracks, which used pigs in a medical training exercise last summer, referred all questions to the U.S. Army Medical Command in Washington, D.C., which was not available for comment last night.

In its complaint, PETA said the animals may not have had access to fresh air, adequate food and water or veterinary care, and they might have been forced to live amid their own urine and feces. The group also alleges possible failure to ensure appropriate ventilation and ambient temperature control in animal-transport containers, failure to provide adequate food and water to animals, failure to ensure hygienic living conditions for animals, and failure to minimize pain and suffering of animals during transport.

“;Not only are these pigs killed in archaic training exercises, some of them may also be suffering and dying even before they arrive at Schofield Barracks,”; says PETA Director of Laboratory Investigations Kathy Guillermo.

Hull said that Matson requires that trained livestock tenders, hired by the shipper, accompany all livestock that are transported aboard its vessels and are responsible for their care while at sea.

“;We work closely with these livestock tenders by providing room and board while at sea and full access to the livestock during the voyage to ensure they can properly oversee the health and welfare of the live animals throughout the ocean portion of the transportation process,”; Hull said.

“;Matson provides water, proper ventilation and convenient stowage for feed supplied by the shipper. Upon arrival in Honolulu and the West Coast, the shipments are given priority status for discharge and special gate hour privileges, in order to expedite the delivery of livestock shipments to the consignee.”;

In July, despite a call by PETA to cancel the training, the Army held the exercise in which live pigs were shot and soldiers learned emergency lifesaving skills by treating the wounds. Army officials said the exercise was essential for training war-bound medics on how to treat critical injuries in combat.