Jan. 26, 2010  -- Undercover videos produced by animal rights groups are fueling a debate over the need for new laws to regulate the treatment of American dairy cows.

The graphic videos include one made inside a huge New York dairy operation where cows never go outside, have the ends of their tails cut off in painful procedures without anesthesia, and are seen being abused by one employee who hits a cow over the head with a wrench when it refuses to move.

An investigator for the group Mercy for Animals worked at the New York dairy farm, Willet Dairy, one of the largest in the state, for two months as a mechanic. Willet supplies to Leprino Foods, based in Denver, which produces mozzarella cheese and other cheese products that are used at chains including Pizza Hut, Papa John's, and Domino's.

"These animals are really treated as little more than milk-producing machines," said Nathan Runkle, executive director of Mercy for Animals. "The overall environment at this facility was really a culture of cruelty and neglect."

Portions of the video will be played in reports to be aired this evening on ABC World News with Diane Sawyer and later on Nightline.

(CLICK HERE AND HERE TO WATCH VIDEOS THAT INCLUDE THE UNDERCOVER FOOTAGE)

The practice of cutting off the ends of the tails of dairy cows -- known as tail docking -- is found in about half of American dairy farms, according to a 2002 U.S. Department of Agriculture report, although a dairy industry trade group says it is in decline.

The practice was banned in California last year and a bill to prohibit tail docking was introduced last week in the New York legislature.

"Science has shown repeatedly this practice is barbaric and totally unnecessary," said Jennifer Fearing, California director of the Humane Society of the United States, which helped push the passage of legislation in Sacramento.

The dairy trade group says tail docking helps prevent cows from spreading manure and filth with their tails in barn conditions.

"I don't think it would help to create an army of tail police to go around and check whether some cows have portions of their tails cut off," said Chris Galen of the National Milk Producers Federation.

Galen said it is in the self interest of dairy farmers to treat their cows well. "The humane treatment of cows, keeping cows as comfortable as possible, definitely has an impact on milk quality," said Galen.

At the Willet Dairy, in East Genoa, New York, the farm's chief executive officer, Lyndon Odell, said the operation produces high-quality milk and does not tolerate the abuse of animals.

"Our animals are critically important to our well being, so we work hard to treat them well, to treat them medically when they need to be treated, to ensure their lives are good while they're here," said Odell.

Shown the undercover videos made by Mercy for Animals, Odell said, "They picked out a few isolated incidents and they're trying to portray them as something that is malicious on our part, that we don't do a good job with our animals."

Odell said he would not hesitate to fire any employee who mistreated one of the farm's dairy cows.

"We have a history of firing people who have mistreated animals because that is not where we belong," said Odell.

The Willet Dairy ships 40,000 gallons of milk a day, mostly to New York City.

Odell says large dairy operations like his, called "factory farms" by animal rights groups, need the large scale to be able to afford expensive equipment and the necessary workforce.

Animals rights groups say the big operations create abuse. "Every single time that we send investigators undercover into America's factory farms, they emerge with startling evidence of animal cruelty and neglect," said Runkle of Mercy for Animals.

"We really think that this goes hand in hand and is inherent in industrial animal agriculture where these animals are really being treated and viewed as little more than production units," he said.

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