From: http://endor.hsutx.edu/~obiwan/profiles/nuer.html (http://endor.hsutx.edu/%7Eobiwan/profiles/nuer.html)
Cattle play an important part in Nuer religion and ritual. Cows are dedicated to the ghosts of the owner's lineages and any personal spirits that may have possessed them at any time. The Nuer believe they establish contact with these ancestor ghosts and spirits by rubbing ashes along the backs of oxen or cows dedicated to them, through the sacrifice of cattle. No important Nuer ceremony of any kind is complete without such a sacrifice.
The Nuer have a traditional religious worldview usually called "animistic." But they worship a supreme being called Kowth who has various manifestations with which some claim to have personal relationships. The Nuer pray for health and well-being, offering sacrifices to Kowth so he will answer their petitions. There is no organized religious hierarchy or system, but many individuals serve as diviners and healers.
They do not believe in a place of afterlife for the spirit, and their religious concepts deal with concerns of this life. They do believe the spirits of the dead can affect their current life. The more recently deceased, the more influence they have. The Nuer honor and appease the spirits of their ancestors. Cattle are sacrificed to God and the spirits.