Authorities in two South Dakota counties have impounded hundreds of horses residing at a wild horse sanctuary operated by the International Society for the Protection of Mustangs and Burros (ISPMB). The impoundment is part of an ongoing investigation into allegations of maltreatment at the facility.

Earlier this month former ISPMB employee Colleen Burns accused sanctuary operator Karen Sussman of maltreating horses at the facility and alleged that 30 animals had died of malnutrition. Sussman denied the accusations.

A representative for the Dewey County, South Dakota, Sheriff’s Department said an investigation was underway.

On Oct. 11, Dewey County State’s Attorney Steven Aberle and Ziebach County State’s Attorney Cheryl Laurenz-Bigue appeared before Circuit Court Judge Jerome Eckrich to request that the mustangs, burros, and other horses at the sanctuary be placed in the care of county law enforcement authorities, court records said