WASHINGTON (AP) – ­­ ­­ ­An animal advocacy group released video footage Wednesday of sick or injured dairy cows that it contends were mistreated at an auction facility where they 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 an 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.

The facility’s owner said he was certain that there was “no way” a downer cow could have gotten into the food supply.

According to the video shot by an undercover investigator for the Humane Society, some of the cows were prodded or dragged by chain that was pulled by a tractor.

The investigator, who worked at the auction 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.”

Pacelle’s group released video in January that was made inside a California slaughterhouse, also shot during an undercover investigation. That footage led to the nation’s largest beef recall.

In May, the Humane Society released video of downed cows being abandoned or mistreated at four auction facilities around the country.

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 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 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 Pacelle’s claim that these filmed incidents are not isolated.

“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.

Messages left for the New Mexico Livestock Board were not immediately returned Wednesday.