Here's a nice possible storyline for it, suggested by Sinest-
<Sinest> -He didn't want to marry her, though, she was beautiful, she was not the complete figure of beauty that he desired, though, as a lord, he was put into a situation where it would mean increased domiance over the countryside, after the marriage, perhaps he would have little to do with her. - -Everything went off without a hitch, and she was his, and he, enjoyed tormenting her, for her smaller breasts, with his control over her lands, he hardly needed her to even be seen by the public, so she, was kept on a short chair to his bed post, where he fully believed she belonged-
<Sinest> -It wasn't until one of his sages approached him, having devised things that could be added to animal feeds to cause live stock to lactate, taking away the need to breed them in order to have productive sources of milk to feed his growing empire that his mind spring to the idea, surely she only befit for his cock, might better serve him in other regards aswell.
<Sinest> -The potion was mixed to the slop of which he allowed her eat from a little dish on the floor, after servicing his cock, and given the proper begging for food, as she shivered with hunger and thirst. The changes were not immediant, over several weeks he had noticed the growth of her breasts, and soon, they became more acceptable to him, as he mashed larger handfuls in his grasp while sundering her many delicate holes- ...
<Sinest> ... -When she began to lactate, it added a further thrill for him, as he enjoyed debasing her, and even brought in stable hands to milk her -udders- while he watched, and cuddled a slave girl into his lap