The massive headgear of deer, cattle, and rhinoceroses raises a simple question: can the animal actually feel these structures? The answer is complicated because these projections are not all the same. Whether an animal can sense its horns or antlers depends entirely on the specific tissue composition and its current stage of growth. Feeling is present in some forms of headgear but almost completely absent in others.
Horns, Antlers, and Rhinoceros Horns: Defining the Structures
Distinguishing between the three main types of cranial projections is key to understanding sensation.
True Horns
True horns, found on animals like cattle, sheep, and goats (Bovidae), are permanent structures composed of two distinct layers. The core is living bone fused to the frontal bone of the skull. This core is covered by a dense outer sheath made of keratin, the same protein found in human fingernails and hair.
Antlers
Antlers, unique to the deer family (Cervidae), are temporary and shed annually. These structures are solid bone throughout, growing from permanent bony bases on the skull called pedicels. Unlike horns, antlers typically branch and are regrown larger each year, making them one of the fastest growing tissues in the animal kingdom.
Rhinoceros Horns
Rhinoceros horns represent a third, separate category, as they are not true horns. These projections lack a bony core, consisting only of a tight mass of keratin fibers. Their composition is similar to an extremely dense bundle of hair, and they grow continuously from the skin of the snout.
The Science of Sensation: Feeling During Growth and Maturity
The different compositions result in dramatically different levels of sensation.
Sensation in Horns
The dense keratin sheath covering a true horn is dead tissue; the outer surface cannot register touch or pain. However, the inner bone core is alive and highly vascularized, extending directly from the skull. Sensation is concentrated almost entirely at the base of the horn, where the living bone meets the skin. A deep injury reaching the bony core or the attachment point would be painful. The animal feels a blow transmitted through the horn to the sensitive base, rather than feeling the tip itself.
Sensation in Antlers
Antlers have the most complex sensory story, changing with the seasons and their growth cycle. The mature, hard antler is calcified, dead bone and completely insensate. However, the structure is highly sensitive during its growth phase when it is covered in velvet. Velvet is a fuzzy skin richly supplied with blood vessels and nerves. These sensory fibers regenerate each year, making the growing antler sensitive to touch and injury. Once fully grown, the velvet dries, dies, and is shed, leaving behind the hard, insensitive bone. This explains why a deer in velvet is cautious, avoiding contact that could cause pain.
Sensation in Rhinoceros Horns
Since a rhinoceros horn is made only of keratin, it is insensate, similar to clipping a fingernail. The animals do not feel the horn itself, and it can be shaved or trimmed without causing pain. Any sensation is limited to the skin and soft tissue at the horn’s base, where living cells produce the compacted keratin fibers.
Proprioception and Damage: The Functional Need for Sensation
The limited areas of sensation are biologically necessary for the animal’s function. The sensitivity at the base of true horns and the temporary sensitivity of antler velvet provide the animal with proprioception, or spatial awareness. This feedback helps the animal gauge the size and position of its headgear when navigating or preparing for a fight.
Sensation at the attachment point is also a mechanism for registering damage to the underlying skull structure. When a bighorn sheep clashes horns, the force is transmitted through the insensate keratin and bone. However, the living tissue at the base allows the animal to perceive the impact’s severity. This perception is essential for determining if a blow is a glancing strike or a debilitating injury to the pedicle or skull.