Sheep are subject to injuries and painful foot diseases, but you very rarely see a limping sheep. Why?
Sheep, like many other prey animals that live in herds, mask their disabilities as much as possible. Predators tend to single out prey that are injured, since they are easier to catch. By masking their pain, they increase their chance of survival. That does not mean that sheep don't limp, just that if you see a sheep limping, it is either REALLY in pain, or it has a damaged leg that prevents it from walking normally.