In Nightjohn by Gary Paulsen, what is Alice used for on the Waller plantation?

On the Waller plantation, Alice is used as a breeder.

In the book, Sarny relates that Alice initially worked as a field hand, "picking and hoeing." As Alice is "addled in the head," Mammy surmises that the master will eventually sell her off. However, because Alice is well-built and physically attractive, the master decides to use her as a breeder. Breeders are slaves who are used to birth more slave babies for the plantation.

Waller has set aside a breeding shack so that male and female slaves can be forced to mate. Sarny relates that Alice takes poorly to the humiliating work of being a breeder, and she reports that Alice becomes badly traumatized as a result of the experience. When she is caught wandering near the white house, the master takes Alice to the spring house, where he whips her viciously.