If an equine is taking narrow, shortened steps while walking behind its leader, what is the most likely issue?

When an equine is taking narrow, shortened steps while walking behind its leader, arthritis is likely the issue. Arthritis can result in pain and decreased range of motion in the joints, leading horses to adjust their gait to minimize discomfort. This adjustment often manifests as shortened strides, as the horse may tense its muscles and make smaller movements in an effort to alleviate pain.

The other options represent different conditions that could impact a horse's movement. Abscesses typically cause a sudden, acute pain that can lead to lameness, but they may not consistently cause the specific gait change of shortened steps. Sidebone, which involves calcification of the cartilage in the hoof, can lead to discomfort but often results in a different gait characteristic, not necessarily the short steps seen in arthritis. Navicular disease involves ongoing pain in the foot but usually presents with a characteristic toe-first landing or other signs of lameness rather than just shortened strides. Therefore, for the symptoms described, arthritis is the most plausible explanation for the horse's gait.