Researching a slave right now whose duties included taking care of the livestock on a farm, and it occurred to me that I haven't read much about horses in sub-Saharan Africa. And while East Africa has cows, they don't seem to figure prominently to the west. I know guineafowl were domesticated, but otherwise, what kind of livestock would a sub-Sarahan West African of the mid-18th century be familiar with before coming to America?
It depends on where you are looking. For examply, in Senegambia cattle was a major parts of the economy as a source for food, as well as for their hides. Horses were much rarer in Senegambia, and were not used in agriculture. They were reserved almost entirely for warfare, and were often paired with particular elite warriors. Donkeys, camels and oxen also were common enough that msot Africans sold to Europeans trading in Senegambia would have been familiar with these animals (Curtin, Economic Change in Pre-Colonial Africa; Barry, Senegambia and the Atlantic Slave Trade).
What do you know about the African origins of the person you are studying?