Ranch Boss by Bruce Corwin

'Meet Carol Lawson, a strict disciplinarian who gloried in dominating men under her cruel power. The owner of a large horse ranch, she turns it into a bizarre harem of men and women, each appointed to satisfy her abnormal urges. She enslaves innocent Jeff Chambers, turning him into a masochistic stableboy and forcing him to participate in perverted orgies - in her bedroom, in the barn, out in the fields, before peeping eyes...... Seeking more kicks, dominant Carol turns to lesbianism, finding Pamela Jenkins 'as satisfying as any man'. Then Carol is the 'male' half of another lesbian relationship with Joan Smith, a switch-hitter who has an abnormal passion for sharing the forbidden rites of sado-masochism....'