I often read that black slaves in antebellum America were treated "like animals". If this was literally 100% true, then I think their white masters would have subjected them to selective breeding programs to create more practical strains of Negro the way they bred more practical strains of dog and cattle. Was this practiced, to what extent, and to what effect?
The first account that comes to mind is the following event of 2 October 1638, which is recorded by John Josselyn in his book Two Voyages to New England. During his stay, Josselyn was a guest in the Boston home of Samuel Maverick - a wealthy land owner and one of the first recorded slave owners in New England (the first recorded arrival of African slaves in New England is February of 1638). Josselyn mentions the following event:
... the Second of October, about 9 of the clock in the morning, Mr. Mavericks Negro woman came to my chamber window, and in her own Countrey language and tune sang very loud and shrill, going out to her, she used a great deal of respect toward me, and willingly would have expressed her grief in English; but I apprehended it by her countenance and deportment, whereupon I repaired to my host, to learn of him the cause, and resolved to intreat him in her behalf, for that I understood before, that she had been a Queen in her own Countrey, and observed a very humble and dutiful garb used towards her by another Negro who was her maid. Mr. Maverick was desirous to have a breed of Negroes, and therefore seeing she would not yield by perswasions to company with a Negro young man he had in his house; he commanded him will'd she nill'd she to go to bed to her, which was no sooner done but she kickt him out again, this she took in high disdain beyond her slavery, and this was the cause of her grief.
(For a great analysis see Wendy Warren's The Cause of Her Grief: The Rape of a Slave in Early New England.)
While this enslaved woman's reported status as royalty in her own society may or may not have had a role in her being chosen by Maverick for breeding, and we have no record of her life besides these few lines, it does show that at this early point slave owners were already partaking in the notion of chattel slavery. Within colonial society rapists could face execution - yet within his home Maverick saw no issue with forcing one of his enslaved people upon another for the sake of furthering his own agenda.
I've heard of similar cases of intentional breeding of slaves elsewhere and at later times, but off the top of my head I can't recall any of them individually.