(Adds Tyson closure, Army Corps dam management, comments from interest groups)
By Theopolis Waters and Tom Polansek
CHICAGO, Oct 7 (Reuters) - Smithfield Foods Inc will shutter a North Carolina hog processing facility, the world's largest, on Saturday to protect employees from Hurricane Matthew, a supplier said, as farmers braced for the storm's potential lashing.
On Friday, Tyson Foods Inc, the biggest U.S. meat processor, closed a plant in Jacksonville, Florida, as Matthew hit the state with howling winds. The facility will remain shut on Saturday, company spokeswoman Caroline Ahn said.
Matthew has fueled concerns about the safety of livestock and farm workers along the coast from Florida through Georgia and into North Carolina and South Carolina. It is the fiercest cyclone to affect the United States since Superstorm Sandy hit the Northeast four years ago.
Smithfield, the world's largest pork processor and hog producer, declined to comment on operations at its plant in Tar Heel, North Carolina. Farmers deliver hogs to the plant, where they are processed into pork chops and bacon.
John Prestage, whose family owns North Carolina-based Prestage Farms, which is contracted to sell hogs to Smithfield, said Smithfield cancelled Saturday's slaughter. He said he expected processing to resume on Monday.
Shutting the Smithfield plant could mean farmers who deliver hogs there will be paid less because the closure will create a backlog of the animals in the region, said Steve Meyer, pork analyst at Indiana-based EMI Analytics.
The plant has a daily slaughter capacity of 32,500 hogs, according to National Hog Farmer magazine.
Separately, environmentalists said they were concerned Matthew could lead to spillages of hog waste held in pits on farms or to farmers improperly spraying manure on wet fields, where it could run off into waterways.
Ahead of Matthew's arrival, Smithfield, owned by China's WH Group Ltd, has been lowering hog waste levels as needed in pits on its farms, company spokeswoman Keira Lombardo said.
The U.S. Army Corps of Engineers' Wilmington, North Carolina, district reduced water releases from two dams on the Cape Fear and Neuse rivers ahead of the storm, said water management chief Tony Young. The goal was to avoid adding to expected downriver flooding problems nearer to the coast.
In 1999, a deluge from Hurricane Floyd "created an environmental and public health crisis" for coastal North Carolina as the open-air pits full of waste spilled into waterways, according to the Environmental Working Group, a nonprofit research organization.
Deborah Johnson, chief executive of the North Carolina Pork Council, which promotes the hog sector, said producers would follow rules that require excess space in waste pits to avoid overflows. She also said they would not improperly spray waste on fields.
Still, about seven people affiliated with Waterkeeper Alliance, an environmental group, spent hours driving around eastern North Carolina on Friday searching for farmers spraying fields with hog waste during a flood watch, a violation of state rules.
Members of the group, known as "riverkeepers," typically like to conduct their checks from airplanes because it is easier to spot violations, said Rick Dove, a senior adviser to the alliance. Cloudy weather kept them grounded.
Additional reporting by Karl Plume and Heiwon Shin in Chicago; Editing by Jeffrey Benkoe and Matthew Lewis