Abstract
The monthly hoof horn production rate, monthly horn loss and the quality of the coronary
horn was examined in the dorsal part of the hoof capsule of Przewalski horses. In order to
demonstrate alterations induced by domestication, the results of this study were then
compared to related data on the hooves of domestic horses in the literature and a concurrent
study on the hoof of warm-blooded horses (KÖNIG, in preparation).
The horn production rate and the horn loss were measured on the hooves of 15 Przewalski
horses. The hooves were marked, and each month the downward movement of the markers
towards the distal margin of the hoof capsule was measured over a period of two and a half
years. The annual mean values of the examined wild horses lie within the standard variation
of the values published for different domestic horse races. But a domestication-related effect
can still be detected, because the values of the Przewalski horses, which were kept in a semi-reservate,
show more seasonal variations than those of domestic horses. This difference
between domestic and wild equides is most likely derived from the different housing
condit ions.
In the examined Przewalski horses, both the hoof horn production rate as well as the horn loss
are significantly higher in the summer than in the winter time. The annual variations of the
horn production rate are particularly influenced by the climatic conditions (environmental
temperature and length of day light), but also by the differing seasonal locomotory activity of
the horses and the varying food supply. The loss of horn, amongst others, is influenced by the
seasonal variations in ground conditions, hoof horn quality, locomotory activity and the body
weight of the horses. Another seasonality is apparent in the occurrence of broken-out horn
chips in the hoof weight bearing margin, acting as an additional mechanism for hoof length
regulation in horses which are kept in reservates and thus suffer from insufficient hoof horn
abrasion.
The horn quality was studied on the hooves of 10 Przewalski horses which were kept in semi-reservates
or in zoological gardens. Apart from a material test by mechanical-technical testing
devices, an examination of structural parameters (horn architecture, inter- and intracellular
factors) was carried out. The range of methods covered light-microscopical and scanning and
transmission electron microscopical as well as histometric, histochemical and immuno-histochemical
techniques. In addition, the inter- and intracellular proteins were separated by
gel-electrophoresis, and the cytokeratins were identified immunochemically. In order to
examine the influence of structural parameters on the mechanical-physical horn
characteristics, the results on the horn structure were then related to the results gained by the
material testing methods. The horn quality differs in the different regions of the coronary horn, therefore a
corresponding localisation of sample-taking is the prerequisite for comparative examination
of the horn quality of domestic and wild horses. Keeping that in mind, minor differences in
the coronary horn of warm-blooded horses and Przewalski are detectable. The outer coronary
horn of the examined Przewalski horses is harder than that of warm-blooded horses. In
Przewalski horses, all regions of the coronary horn show a lower water-storing-capacity.
These differences in the mechanical-physical horn characteristics are reflected by an equally
differing horn structure: The coronary horn of Przewalski horses is characterised by smaller
and more densely packed horn tubules which additionally show a decreased cortical-medullar
ratio compared to the respective horn tubules in warm-blooded horses. Even the cyto-architecture
shows differences in both types of horses: in przewalski horses remainders of the
cell nuclei are always present, whereas in warm-blooded horses the cornified cells are mostly
nuclei-free. Comparing the results of the gel-electrophoresis, Przewalski and warm-blooded
horses show a similar protein band pattern, but the staining intensity differs slightly in some
protein bands. The mentioned differences in the horn quality of domestic and wild horses are
mainly induced by genetic factors and may therefore be influenced by selective breeding. An
influence of the housing conditions on the hoof horn quality of Przewalski horses was not
detectable in the examined specimens.
In the examined Przewalski horses, both horn hardness as well as horn structure (horn
architecture and intercellular factors) vary according to the time of horn production. These
seasonal variations in hoof horn quality are correlated to the seasonal variations in the horn
production rate and contribute to the seasonal rhythm of horn abrasion and are also
responsible for the occurrence of broken-out horn chips in the hoof weight bearing margin. |
