A COMPARISON OF HORN QUALITY OF THE WHITE LINE IN THE DOMESTIC HORSE (EQUUS-CABALLUS) AND THE PRZEWALSKI HORSE (EQUUS-PRZEWALSKII)

Using scanning and transmission electron microscopical techniques impr essive structural variations were observed in the two species. In the domestic horse the terminal horn tubules and cap hom tubules situated between the horny leaflets were empty of contents in their centres, so that actual tubular structures occurred. Bacterially decayed hom can be identified with the naked eye as black or chalky white discolourati ons. It should be removed during hoof care and hom cavities should be disinfected with iodoform ether. Stable hygiene is of crucial signific ance. Urea, or a mixture of urine and dung, causes a decrease of horn quality. In Przewalski horse the white line is significantly smaller, the percentage of stabilizing leaflet horn is correspondingly larger a nd the amount of terminal horn is relatively less. These terminal horn ''tubules'' are not centrally empty but are filled by reticular or st ony medullary cells. In this case the term ''tubule'' is misleading. T he intact medullary cells are important for the maintenance of a barri er against ascending bacterial invasion. These barriers are better dev eloped in Przewalski horse than in the domestic horse.