Penthouse magazine definitely put out suggestive cartoons and printed forum stories normalizing casual sex between dogs and pretty girls. Many of the pictorials featuring Penthouse Pets include horses, dogs, ect. No sex, but it feels implied. Not surprisingly, it has been revealed on multiple media outlets that Penthouse owner Bob Guccione had an obsession with the subject, so makes sense he would attempt to excite his readers by photographing beautiful women with animals.
Incidentally, Playboy owner Hugh Hefner had a long history of fixating over dogs. That is pretty well documented.