WASHINGTON — An animal advocacy group released undercover video footage Wednesday of sick or injured dairy cows that it contends were mistreated at an auction facility where cattle are sold for slaughter.

Three cows too sick or weak to stand were sold at the Portales Livestock Auction in Portales, N.M., the Humane Society of the United States said. Such cows pose increased risk for mad cow disease, E. coli and other infections, partly because they typically wallow in feces and their immune systems often are weak.

But the facility's owner said he was certain that there was "no way" a so-called downer cow could have gotten into the food supply, and a top federal official agreed.

More on the story below this video from The Associated Press, broadcast June 25, 2008. Warning: some viewers may find this video disturbing.

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In January, the Humane Society released undercover video from a California slaughterhouse that led to the nation's largest beef recall. In May, the group released video of downed cows being abandoned or mistreated at four auction facilities around the country.

According to the latest Humane Society video, some cows at the New Mexico auction facility were prodded, or dragged by a chain being pulled by a tractor. The investigator, who worked at the facility in May, claims to have observed three downed cows sold after being brought into the auction area by force.

"At every turn, we have found appalling abuses of spent dairy cows," said Wayne Pacelle, the Humane Society's president and chief executive. "No longer can anyone in government, or in the livestock industry, claim that this is an isolated abuse."

The Portales facility is owned by Randy Bouldin. He also owns the Livestock Exchange in Hereford, Texas, which was one of the targets of the society's May investigation.

Bouldin said that there are strict policies in place at both his sale barns to handle downer cows and that they have spent all day refreshing the employees' knowledge of these policies.

"But in no way did a downer cow go into a food supply or to a packing house," he said. "I'm certain that there's no way that could have happened."

Agriculture Secretary Ed Schafer, who saw a preview of the footage Tuesday, agreed.

"It is evident that these cattle were too weak to rise and walk on their own and would not have been accepted upon delivery to a slaughterhouse," he said. "The condition of these cattle would prohibit them from even entering the first phase of a multi-phased process of approving cattle for slaughter."

John McBride, spokesman for industry trade group the Livestock Marketing Association, disagreed with the Humane Society's claim that the filmed incidents represented widespread practices in the industry.

"You have to put this in context of the number of cattle handled in markets annually," McBride said.

Across the country in 2006, 1,200 livestock marketing businesses handled 35.6 million head of cattle and calves, according to government figures cited in a release from the Texas and Southwestern Cattle Raisers Association.

Auction facilities are not subject to federal government inspections. The Humane Society investigator said New Mexico state inspectors were on site when some of the abuse took place.

Myles Culbertson, director of the New Mexico Livestock Board in Albuquerque, N.M., said inspectors are usually outside the entrances of these markets, watching cattle as they enter a facility, not observing the auction ring. He said he doubted that a downer cow could be sold at auction, because it would have to walk in and out of the ring.

"A buyer at a sale ring is not going to buy a cow that's not ambulatory," he said.

Culbertson said the board plans to investigate the issues raised by the Humane Society video.

Associated Press writers Betsy Blaney in Lubbock, Texas, and Sue Major Holmes in Albuquerque, N.M., contributed to this report.