Page 297 - Anatomy and Physiology of Farm Animals, 8th Edition

282 / Anatomy and Physiology of Farm Animals

Chapter 8. The following is a brief over- Horns
view of the anatomy of the hoofs of artio-
VetBooks.ir dactyls, the even‐toed ungulates. Horns of cattle and sheep are formed over

A convenient terminology for the digits
of even‐toed animals is to refer to the dig- the cornual process, a bony core that pro-
jects from the frontal bone of the skull
its by number (III and IV in ruminants (Fig. 14‐8). Both male and female cattle of
and pigs), and then relate each digit to the horned breeds have horns, although the
midline of the respective foot. The axial female animal’s horns are smaller. In most
side of the digit is the side closest to the horned sheep and goat breeds, both males
midline of the foot and the abaxial side is and females have them, although in a few
the side farthest from the midline of breeds only rams or bucks are horned.
the foot. Animals that lack horns naturally are polled.
The hoof wall consists of a nearly verti- The corium of the horn completely envel-
cal axial portion that reflects sharply cau- ops the cornual process and blends with its
dad at the toe (tip of the hoof) to be periosteum. The horn itself consists of dense
continuous with the abaxial portion of the keratin, much like the hoof wall, and elon-
wall. The abaxial hoof wall is convex and gates from the base. A soft type of horn
the axial wall is concave, and both the axial called the epikeras covers the surface of the
and abaxial surfaces are continuous with horn at the base and extends a variable dis-
the bulb of the hoof. The lateral digit bears tance toward the apex of the horn. The
more weight than the medial one (as a epikeras resembles the periople of the hoof.
clinical consequence, most foot lameness Variations in level of nutrition of the
in dairy cattle is referable to the lateral animal are reflected in variations in rapid-
hoof). In contrast to the horse, the sole ity of horn growth, resulting in a series of
and bulb of the foot carry a great deal of rings on the horn. These alternations in
weight relative to the walls and toe. The thickness of the horn may reflect seasonal
bulb of the porcine hoof is especially stresses, notably the stress of calving in
prominent, providing a larger proportion cows. The age of a cow bearing calves
of the weight‐bearing surface than in annually may be estimated by counting the
ruminants. rings on the horn.

Horn
Haired skin

Combined corium
and periosteum

Cornual diverticulum
of frontal sinus

Figure 14-8. Longitudinal section of a horn. The horn is supported by a bony core, the corneal process
of the frontal bone, which is invaded by a diverticulum of the frontal sinus. Periosteum and corium are
blended on the surface of the cornual process.