Eighteen bighorn sheep (Ovis canadensis) with known or suspected contact with domestic ruminants on public or private land were removed to prevent possible disease transmission. Live bighorns maintained in captivity were monitored for evidence of respiratory disease. Contacts with cattle (n = 4) occurred in December, January, and July; whereas, most contacts with domestic sheep (n = 10), goats (n = 3), or both (n = 1) occurred between April and October. Four bighorns died within 7 days following capture and 10 survived from 47 days to 57 months in captivity. Five bighorns had gross and/or histological evidence of pneumonia. Pasteurellaceae were isolated from 17/18 bighorns, and domestic ruminants that were contacted by 4 bighorns. Isolates included multiple biovariants of Mannheimia spp. and Bibersteinia trehalosi, and Pasteurella multocida subspecies and biotypes. Pasteurellaceae from pneumonic lungs included Mannheimia spp. biovariant 1, P. multocida subsp. multocida a, and B. trehalosi biovariant 2B. The Mannheimia spp. biovariant 1, isolated from 2 pneumonic bighorns and contacted domestic sheep, had restriction fragment-length pattern similarity coefficient values of 1.0, indicating high similarity and likely sharing between the species. Management implications include the need for species separation and rapid responses to contact situations because 28% of the bighorns died with evidence of respiratory disease following domestic ruminant contact. © 2014 The Wildlife Society.