Happens here too, most commonly giraffe chew bones. ( no shed antlers in Afica!) Antelope like eland and kudu as well. Cattle also chew bones. The general concensus is that they chew them for the minerals, especially calcium. Interestingly after a veld fire many differnt species of grazing and browsing animals will gather to lick up the white burnt ash of trees and grass clumps. Zebra are quick to move to a burnt area. Same thing as a mineral lick, ash is pure mineral, no fibre and no water.
Is there such a thing as a real vegetarian given that humans are reputed to swallow at least fifty spiders in their sleep per year?
chrisg