Just a basic idea to developed further.
Gwen led her troll through the crowded market. He was a gorgeous one, tanned and well portioned in legs, rump, and chest. His golden head of hair was full and flowed lightly over his muscular strong shoulders. His eyes were a sky blue. He was a man-troll named by Gwen when her mother purchased him for her daughter on her sixteenth birthday. His name was Sky.
Being her beast of burden, protector, and slave, she had dominances over him completely. As all trolls, he had been raised from a pup and surgically correctly to be as he was today, a docile, simple creature. Once a proud male of the human race, now, as all others, just a troll. All males are these simple creatures. It had been decided long ago by the now feminine matriarchal society as best for peace and tranquility of life.
Man had proven his warlike nature over and over again until he literally destroyed his civilizations. What emerged from the dust and vast destruction came a simpler world dominated by females. Men, at first, were less then one in eight of the population and even declined further. That was nearly one hundred years ago.
Now, after much study and medical experimentation man was under control and his numbers had stabilized at one in four. And though rumors have it that some small numbers of them have been seen hidden the wild-lands the arrangement was working well.