No, they were not. But they were sometimes bred for size and strength. The commercial breeding of slaves was quite rare and rarely documented (but not unknown to occur). But almost all slave owners came to understand that the natural increase of the slave population was profit in the owner’s pocket….rather like “interest on their investment” just like the reproductive value of other livestock. Some agricultural pamphlets reminded plantation owners to include the “natural increase” in their slaves when calculating their annual assessment of profits or losses.
In the “Slave Narratives” interviews that were collected by Congress in the 1930’s from former slaves.still living…several women recount being forced to mate with a man of the owner’s choice and the added value of a female slave who reproduced with regularity. One recounted that he father had been a “stock Negro” who had sired 72 children. There is another account in the Congressional Record (during a debate on slvavery in the mid-1800’s) by a male slave who testified that he had been “purchased by the master in order to increase the quality of of the black children born on his plantation. Another account given in the early 1900’s by a former slave, Robert “Uncle Bob” Wilson, who had fought in the civil war, claimed that as a young man he had sired 300 children (often having been rented out to neighboring slave owners as a “stud” for $10). Wilson died in the Elgin State Hospital for Veterans in Illinois in 1948 at age 112.