Cattle
The cow is a species of large, formerly domesticated ungulates originally from the Middle East. After collapse, surviving cows went feral.
#Human relations
People of the Fifth World will sometimes hunt herds of feral cows for meat and make clothing - and sometimes houses - from their skins. More rarely, when specializing in relationship with cows (see below), they may milk them.
#Specialization
A community that specializes in relationship with cows will likely follow the semi-feral herds as they travel, possibly going so far as to burn out fields for them to graze in. Like other nomadic cultures (e.g., Mongolians or Plains Native Americans), they would likely live in collapsible houses made of animal skin. Such a community may also specialize in relations with horses, befriending and riding them from place to place. (Of course, in the Fifth World, each individual relationship between horse and human rider would have to be kindled and maintained; one would never enslave a horse and force them to do one's will. Therefore, not everyone would ride a horse, and even if a person befriended one horse well enough that they would agree to being ridden, after that horse died, there would be no guarantee that that person could build a similar relationship with another horse.)
A community specializing in relationship with cows may have a tradition wherein certain people manage to so closely befriend individual female cows that the cow allow them to milk them. One such tradition may limit only children to this task (maybe young girls, in vague memory of milkmaids), as milk of any kind is generally meant only for babies. Regardless, the consumption of milk or milk products by adults is very rare in the Fifth World. Milking animals, and making butter or cheese from that milk, would make this community fairly unique. Naturally, a community that consumes dairy products would need containers in which to keep and ferment the milk; while dried gourds or coconut shells could work for that purpose, such a community may additionally practice pottery. This may require living near a source of good clay, and spending part of the year in a camp there, making their pottery.
Communities that practice a form of Hinduism are more likely to specialize in relationship with cows, but will never kill them for meat unless their variation on Hinduism has diverged wildly from the religion's historic viewpoint on these creatures.