WASHINGTON - The Interior Department abruptly halted delivery of mustangs to buyers while it investigates the slaughter of 41 wild horses at the Cavel International plant in DeKalb this month. By enlisting last-minute financial help Monday from Ford Motor Co. - makers of the Mustang sports car - the agency saved the lives of 52 other mustangs. The latest horses killed came from a broker who obtained them from the Rosebud Sioux Tribe of South Dakota. The tribe traded 87 of the 105 aging horses it bought from the government for younger ones. Interior officials said they would review whether a federal contract had been violated. Tribal officials were unavailable for comment. "I don't think it's fair to say they violated the agreement," Kathleen Clarke, director of Interior's Bureau of Land Management, told The Associated Press. "They were not trading to the animal processing facility. They were trading to a private individual." The Sioux tribe had to sign an agreement with BLM that it would "provide humane care" to each of the animals, documents show. Clarke said Interior's top lawyer was investigating that arrangement. The department also is investigating this month's sale of six wild horses to an Oklahoma man and their slaughter at the Cavel plant, the same place 35 of the 87 horses traded by the tribe were killed. "It's incredibly disappointing," Clarke said. "It is not our intent to have these animals killed. That's why we acted very aggressively." Congress in December replaced the 34-year-old ban on slaughtering mustangs with a law permitting older and unwanted horses to be sold. Wild-horse advocates warned that will allow the animals to be killed and sold for horse meat, as dog food or for people to eat overseas. "Horses that were free for 20 years are now being captured in a completely strange situation and subject to being killed," Trina Bellak, president of the advocacy group American Horse Defense Fund, said Monday. BLM officials, tipped off by Agriculture Department inspectors, on Monday persuaded the plant managers to stop the slaughter of the horses formerly under the control of the BLM. That saved the lives of 16 mustangs about to be killed. The plant agreed to give the horses food and water until BLM officials could arrange to have them picked up, which happened this morning, according to Cavel General Manager Jim Tucker. He wasn't sure where the horses were headed but said the trucker who took them was from southern Illinois. The 16 horses as well as the others that came with them that were slaughtered had just arrived at the plant on Monday, he said. He said all the horses from the BLM program that were slaughtered were older and of no use anymore. Tucker said Cavel had not yet paid for the horses that were saved. That is done after slaughter and is based on carcass weight. BLM spokeswoman Celia Boddington said last week that a new federal law allows for the slaughter of the unwanted BLM horses, but that the agency has been implementing the law with the intention of making sure the horses are adopted by owners who intend to keep them alive. "I think what the problem is is that they (BLM) want to encourage people to adopt horses and they don't want to be seen as giving away horses just for slaughter," Tucker said. To the agency, having the wild horses slaughtered is a "public relations problem," he said. BLM officials also intervened to save 36 mustangs in Nebraska that were on their way to the Cavel plant. Those horses were to be picked up separately today and kept in the Midwest. BLM, which captures the animals during government roundups aimed at reducing the wild population, has sold and delivered nearly 1,000 horses since the new law passed. BLM says 37,000 wild horses and burros forage its lands, 9,000 more than Western ranges can sustain. Clarke said she ordered an immediate halt to the delivery of some 950 more horses that have been sold. "We will not be making any more deliveries until we can check on the situation," she said. "We just want to reassess our program." Clarke said she'd already been talking with Ford about such a partnership even before she called the company for help Monday. "We do not have any clear authority to buy private animals," Clarke said. She persuaded Ford to pledge $19,000 to ship and care for the mustangs. Daily Chronicle City Editor Chris Rickert contributed to this report.