These are just dead cows (?) I think, maybe, the gameworld was designed before the final gameplay was finished. Early plans were that the monster hunt was much more realistic, for example with weakness-spots, which you could examine with the withcer senses, blood trails, if the monster was wounded, and so on. Maybe the dead cows were used kinda as a trail for certain monsters.
I think the grave stone is a part of the spirit under the tree quest. If you decide to help the spirit you have find her bones and burn them I think. I'm not sure though.