Thirst, by Rod Hardy (1979)

Kate Davis, a pretty young woman, finds herself in the sights of a mysterious organization whose members inexplicably have her kidnapped. She’s taken to a tiny village nestled in a remote forest, a rigidly controlled environment that’s run like a small corporation. Hordes of zombie-like people wander the grounds whose sole purpose is to have their blood sucked and then packaged in milk containers for consumption by members of the Hyma Brotherhood, a group of people with an insatiable thirst for blood (and who dislike the term Vampire). Kate, it seems, is a descendant of Elizabeth Bathory, the notorious real life “Bloody Countess”; the Brotherhood is looking to unite Kate’s bloodline with its own in an effort to ensure their immortality. But first Kate will have to be forcibly brought around to the Brotherhood’s way of thinking. She escapes but is quickly recaptured and subjected to a series of psychological tests designed to break down resistance to her inner vampire. The process appears to work in the Brotherhood’s favour, but it’s all an act on Kate’s part. With the help of the sympathetic Dr. Fraser, Kate manages to escape via helicopter, but in fact the good doctor isn’t nearly as upstanding as he appears…