What qualities about a land-dwelling creature are absolutely necessary to maintain an effective herd of that creature for food and/or resources?
Assume this is an earth-like environment.
The animal must be docile and handlable enough that necessary veternary work, breeding, and transport are possible. No trying to herd dinosaurs when you only have caveman tech; you won't succeed.
The animal must be able to produce enough of a resource or combination of resourcesto overcome the cost of raising it. Aka if you are raising it for wool it must
produce enough to pay for its food (could mean pasture) and provide a living wage.
It is not required but it would be must more cost effective for it to be
herbivorous. If wolves pooped the cure for cancer, we'd raise a herd of them with a herd or two of cattle for support. It would not be easy but it would be possible.
They must not kill each other. (aka herd mentality)
You need some way to confine them.
It is preferred that their lifespan is fast enough that you can
harvest within a year or two of being born. This comes into the cost of raising them, however.
Beyond that I don't think there are any hardfast requirements. You can herd elephants, lions, or dolphins with enough resources, manpower, and income from it but none of these will be as easy as sheep.
Another quality which hasn't been mentioned is the animal's mating practices. Some reference I've read - I believe it was Guns, Germs, and Steel - points out that there are several animals which herd naturally, follow a leader, are of great economic value, but are still not kept domestically because they are very difficult to breed in captivity. I think elephants were the example used.
Most likely (if looking at our own planet and herds) it should be herbivorous. Pigs are the only omnivorous animals I can think of that we keep in herds, and it's debatable if they can really be considered a 'herd'. Herd mentality is where they group themselves together without outside influence, sheep, bison, elk, zebra etc.
The ability to be controlled easily, it helps when the animals responds to and follow a leader.
Six Criteria for Domestication: