Keep that standing rib roast on your Christmas menu – state officials Wednesday assured Maine consumers that beef is safe to eat, despite the nation’s first case of deadly mad cow disease being announced late Tuesday afternoon in the state of Washington.

Nerve tissue from a sick cow at a processing plant was tested at a government laboratory in Iowa, with a presumptive diagnosis of the disease released Tuesday. The tissue specimen has been sent to a British laboratory for confirmation. The result may be several days in coming, but health and agriculture officials are proceeding as though the finding is conclusive.

Mad cow disease, or bovine spongiform encephalopathy, is a degenerative disease that affects the nervous system of cattle, making the brain spongy and full of holes. It is believed the disease can be transmitted to humans by eating meat products from infected animals.

The disease is not well understood, although it is thought to be related to the once common but now-outlawed practice of adding rendered animal byproducts to the grain cattle eat. There is no effective treatment. An outbreak in European cattle in the 1980s and 1990s led to the deaths of more than 100 people and effectively shut down the beef industry there.

In May of this year, a single case of mad cow disease was found in Canada, prompting the U.S. to ban Canadian beef imports for several months.

In a Christmas Eve press release from the Maine Department of Agriculture, Commissioner Robert Spear said beef that potentially could have been contaminated with the factor that causes BSE has been recalled by the processor, and the farm where the lone dairy cow was raised has been quarantined.

“These are necessary and prudent measures to protect human health,” Spear said, adding that his family will enjoy its traditional holiday meal this year, featuring beef as the main course.

Also anticipating a Christmas Day feed of beef was Judy Powell, executive director of the Maine Beef Industry Council.

“This is just one case,” Powell emphasized in a phone conversation, pointing out that stringent federal inspections and regulations have been in place since 1979 to ensure the safety of meats entering the food supply. The single cow with the presumptive diagnosis of BSE, she said, could be a survivor from earlier days before such safeguards were put in place. It’s not uncommon, she said, for a dairy animal to be kept to an advanced age before being sold for low-quality meat.

But while Powell is not concerned about the safety of her family’s holiday meal, she is worried about the impact of the Washington case on Maine’s beef industry. Japan, the largest importer of U.S. beef products, has already halted imports in response to the mad cow scare, as have South Korea, Russia, Thailand and Hong Kong. If demand for American beef is driven down and stays down, Powell said, the impact on Maine’s small growers could be profound.

About 800 farms in Maine include beef animals in their output, with an average of about 25 or 30 animals apiece, she said. The industry has a “farmgate value” of about $60 million a year, reflecting the value of the animals themselves, but the spin-off impact of the industry, including trucking operations, feed suppliers, slaughterhouses and so forth, is much greater. A hit to growers, in the form of lower prices, could create significant ripples in the state’s economy, Powell said.

Maine’s largest beef grower, Carroll Caron of New Canada, said growers will just have to wait the situation out until test results confirm the diagnosis of BSE.

Caron raises 1,300 to 1,800 beef animals each year for Wolfe’s Neck Farm, a Maine-based nonprofit company that markets an “all natural” product. His animals are raised without antibiotics or hormones and their meat brings top dollar from choosy consumers concerned with the safety and quality of their meats, he said. Most of his products are sold through Hannaford stores, an East Coast chain headquartered in Scarborough.

But if BSE is confirmed and import bans stay in place for any length of time, Caron said, prices for all beef could plummet by as much as 60 percent. “For a lot of people, it would put them out of business,” he said.

Most Maine beef growers, including Caron, truck their animals to a large packing plant in Pennsylvania to be slaughtered and processed. But Maine also has a handful of small family-owned abattoirs, or slaughterhouses. Tom Gilbert, owner of Herring Brothers in Guilford, said he doesn’t want to see the mad cow situation “blown up” by the media. But he admits he’s already apprehensive about the impact on his fourth-generation family business.

Fifteen years ago, Gilbert said, Herring Brothers processed at least 100 beef animals a week; now they might do 15, plus a few pigs and lambs. He blames the drop in business on changes in international trade regulations making it easier for Canadian processors to offer better prices.

Most of Gilbert’s business comes from local farmers who raise a few animals for themselves or their neighbors, or to sell at farm stands in the area. Gilbert, who runs a small retail operation himself, said he’s already told his store manager to stop buying beef until the dust settles on the mad cow scare, so he doesn’t find himself selling his inventory for less than he paid for it.

But Gilbert, who, with his grown sons, was hard at work on Christmas Eve, said there wasn’t much else to be done about the situation. “I guess we’ll just sit tight and see what happens over the weekend,” he said.