A horse jaw is not a meat-bearing bone.

Unlike the femur or the humerus, where large muscle groups attach and where most of the meat on a large animal is concentrated, the mandible is a skeletal element of the lower face, associated primarily with the muscles of chewing and with the soft tissue of the face, lips, and tongue.

Why would someone make cut marks on a horse’s jaw?

The answer is found in the specific locations and orientations of the marks.