The Interior Department abruptly halted delivery of mustangs (search) to buyers while it investigates whether the slaughter of 41 wild horses in the West this month violates a federal contract requiring them to be treated humanely.

By enlisting last-minute financial help Monday from Ford Motor Co. (search) — 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 traded 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 (search) to an Oklahoma man and their slaughter at the Cavel International Inc. commercial packing plant in DeKalb, Ill, the same place the 35 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.

Rep. Nick Rahall, D-W.Va., on Tuesday urged Congress to immediately repeal the change in law that Sen. Conrad Burns, R-Mont., sponsored last year. Rahall and Rep. Ed Whitfield, R-Ky., so far have 50 co-sponsors for such legislation in the 435-member House.

"America's love affair with wild horses and burros has turned into a horror story of slaughter and betrayal," Rahall told the AP. "Sadly, slaughter is the inevitable result of the ill-conceived changes in law that occurred late last year."

Whitfield and Reps. John Sweeney, R-N.Y., and John Spratt, D-S.C., also reintroduced a bill that stalled last year and would ban the horse slaughter trade, whether domestic or shipped live for that purpose abroad.

BLM officials, tipped off by Agriculture Department inspectors, on Monday persuaded the plant managers to stop. That saved the lives of 16 mustangs about to be killed.

The plant agreed to give the horses food and water until BLM officials can pick them up. BLM officials also intervened to save 36 mustangs in Nebraska that were on their way to the Cavel plant. Those horses are to be picked up separately Tuesday 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 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.