Page 40 - Adams and Stashak's Lameness in Horses, 7th Edition

6 Chapter 1

VetBooks.ir Primary epidermal laminae

Primary dermal laminae

a b

Secondary laminae

Figure 1.6. Photomicrograph of laminae of the equine hoof. In epidermal portions of the hoof (primary epidermal laminae) are the
the top image, a indicates corium; b is the epidermis (hoof wall). “insensitive laminae.” The box indicates the region enlarged in the
Laminae extending from the corium (primary dermal laminae) are lower image. Here, smaller interdigitating projections, the secondary
the so‐called “sensitive laminae.” Laminae extending from the laminae, can be seen arising perpendicular to the primary laminae.

12 months for hoof generated at the coronary band to immediately internal to the white line that serves as a
reach the ground. The wall grows more slowly in cold landmark for determining the proper position and angle
and/or dry environments. The hoof wall grows evenly for driving horseshoe nails. 14
distal to the coronary epidermis so that the youngest The frog (cuneus ungulae) is a wedge‐shaped mass of
portion of the wall in contact with the ground is at the keratinized stratified squamous epithelium made softer
heel (where it is shortest). Because this is the youngest than other parts of the hoof by its greater water con­
part of the wall, it is also the most elastic, which allows tent. Apocrine glands, spherical masses of tubules in
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it to accommodate heel expansion during concussion. the corium of the frog, deliver secretions to the surface
Stratum medium may be pigmented or nonpigmented. of the frog. The ground surface of the frog presents a
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Contrary to popular belief, there is no difference in pointed apex and central sulcus bordered by two crura.
the stress–strain behavior or strength properties of Paracuneal (collateral) sulci separate the crura of the
pigmented versus nonpigmented equine hooves. It has frog from the bars and the sole. The palmar aspect of the
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also been demonstrated that pigmentation has no effect frog blends into the bulbs of the heels. Compression of
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on fracture toughness of hoof keratin. On the other the frog during weight‐bearing is transferred to the
hand, water content of the hoof significantly affects its fibrofatty digital cushion deep to the heels; this force
mechanical properties. In the natural hydration gradient assists with movement of venous blood from the interior
in the hoof wall, the moisture content decreases from of the hoof capsule to the veins of the distal limb.
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deep to superficial. Very dry or extremely hydrated The corium blends with the periosteum of the distal
hoof wall is more likely to crack than normally hydrated phalanx, serving (particularly in the laminar region) to
hoof wall. A normally hydrated hoof is better able to connect the hoof to the bone. The corium, the hoof’s
absorb energy without mechanical failure. 4 homolog to the dermis of skin, is composed of dense
The slightly concave sole does not normally bear white fibrous connective tissue that is rich in elastic fib­
weight on its ground surface except near its junction ers, highly vascular, and well supplied with nerves. Corial
with the white line, but it bears internal weight transmit­ arterial supply derives from numerous branches radiating
ted from the distal phalanx through the solar corium. In outward from the terminal arch in small canals extending
the unworn, untrimmed hoof wall, insensitive laminae from the solar canal in the distal phalanx and from the
can be seen on the internal surface of the wall where it dorsal and palmar branches of the distal phalanx, them­
makes contact with the ground (Figure 1.3). When the selves branches of the digital arteries (Figure 1.8).
hoof is trimmed, the white line where the wall meets the The coronary and perioplic coria and the stratum
sole is more clearly discerned. The sensitive corium is basale of the coronary and perioplic epidermis constitute