The largest tourist dog sledding operation in the United States has admitted to an Aspen, Colo., newspaper that unwanted sled dogs not given up for adoption are shot in the back of the head and buried in a pit.

The practice is legal under Colorado law, even though some of the dogs that are killed are healthy, the Aspen Daily News reported in its Monday editions.

A former musher at the Krabloonik dog sledding center told the Daily News that he saw dogs shot annually during the years he worked there and that one year, 35 dogs were shot and killed in the culling process.

"I still lose sleep over it at night. I was part of it," Harry Portland told the newspaper.

As many as 250 dogs live at the sledding center and owner Dan MacEachen said dogs are killed with a .22-caliber rifle and buried in a pit after being covered with lime. The same pit is also used to bury collected excrement from the dogs.

MacEachen told the Daily News every year. He also said older dogs are the ones primarily euthanized, but pups and younger dogs incapable of pulling sleds have been killed if homes can't be found for them.

A former employee who worked at Krabloonik in the 1990s told the newspaper that the first year he worked there 27 dogs were shot and tossed into the pit.

The state veterinarian's office said killing dogs by shooting them in the head is within the law, which considers an animal and individual's property that can be euthanized at any time -- provided it is done humanely.