Linea alba unguis (Zona alba) - the white line of the horses hoof in its semi-circumference

Linea alba unguis (Zona alba) - die weiße Linie des Pferdehufes in ihrer Semizirkumferenz

von Zadow C, Budras K-D

DOI: 10.21836/PEM20080301
Year: 2008
Volume: 24
Issue: 3
Pages: 306-312

The structure and composition of the white line in the horses hoof is well documented in the dorsal part. Little is known about structural changes in its semi-circumferent course. The white line of the hoof was investigated in its semi-circumference using light microscopy and morphological techniques. A total of 21 right front hooves of adult horses was analyzed. Previous to sample taking and morphometric evaluation,feet were trimmed according to a defined trimming method and anatomical landmarks were developed in order to obtain comparable results in a reproducible manner. PAS-stained histological slides of seven defined section sites of the white line were analyzed microscopically. Width, height and structural composition of the white line vary strongly according to the area the sample is taken from within the hoof. The white line is widest in the toe region and gets thinner in palmar direction. Primary epidermal lamellae in the toe region are very densely spaced and have a straight appearance. The further palmar the section site, the larger the gap between two lamellae. Palmar the lamellae also get smaller, with a bended appearance. At the same time the amount of soft interlamellar horn increases. This reflects the function of the proximal lamellar junction in the corresponding areas: in the dorsal part of the hoof the suspension of the pedal bone dominates (=weight bearing function), whereas in the palmar part of the hoof the lamellar junction is an elastic anchorage which restricts the collateral outward movement (spreading) of the palmar aspect of the horn capsule. Except for the region of the bars, the apex of the epidermal lamellae always points toward the center of the hoof. Size, amount and arrangement of terminal horn tubules vary a lot in between individual hooves and within the same hoof. In many cases between two lamellae there are additional queues of terminal horn tubules or terminal horn tubules are arranged without any sort of pattern. Especially in the palmar areas the structures of the white line (epidermal lamellae as well as terminal and cap horn tubules) display strong individual characteristics.