Africa is an old continent, and vampire beliefs are much older than the contemporary Christian vampire, but before that, it took on a bit of a different flavor. Still, vampirism, if you want to call it that, always has one thing in common, the draining of life.
It does not actually need to be followed by the rising of the dead, and in African beliefs, is often replaced by disease or ruin. Which I believe must be the origin of vampire folklore, anyways. (even the word ’‘nosferatu’’ is derived from the Greek word ’‘nosophoros’’, which means plague carrier)
That said, I have absolutely no idea what the Massai specifically believe when it comes to vampires. Here’s an interesting article about African beliefs in demons and vampire like fiends, which not only drain the blood of humans and livestock, but also of fruit, and who also steal drinkable water)
Article.
I don’t know how it works in differing African cultures, peoples and tribes, as in if they all share the same beliefs, mythologies or if each group has their own specific sets, but when reading that article, a lot of it seems to resurface. The Massai though, hold cattle as a very important part of their lives. In fact it’s pretty much what defines them. The cow is important and sacred to them, and if they do drink the blood, I don’t think it has anything to do with vampires, as most of their rituals are in a positive light, (I do not specifically know what their rituals are) and often used to lessen the gap between themselves and their deity.