If you mean nomadic pastoralists, then never. They were dependent for survival on their flocks; and the daily management of even a small nomadic flock required several herders. An individual who owned a herd and lacked enough family members to manage it would have to hire availible herders from other families in the tribe—and owning animals would have been a requirement for membership in a tribe.

(Source: an anthropological study of traditional nomads in Persia in the 1950s.)