Shape, Orientation and Spacing of the Primary Epidermal Laminae in the Hooves of Neonatal and Adult Horses (Equus caballus)

Circumferential and proximodistal variations in the morphology of the primary epidermal laminae of six neonatal and five adult equine feet were documented. Three parameters were quantified: interlaminar spacing, the orientation of the laminae with respect to the overlying wall, and any angulation within the laminae themselves (‘internal angle’). In adult feet, the laminae were most closely spaced at the dorsum, the spacing increasing gradually towards the heels. In foals there was a non-significant trend for the dorsal laminae to be more widely spaced than those in more caudal parts of the foot. In both age groups, the dorsal laminae were almost straight (mean divergence from linearity at all sites 2°), and were oriented at approximately 90° to the tangent to the overlying wall (mean orientation for all sites 91°). At the quarters, the laminae were in general oriented caudally relative to the tangential position from their epidermal to their dermal ends (mean orientation of >90° at 12 of 16 sampling sites, where an orientation of >90° defines a ‘caudally directed’ orientation) and, in general, had a bend within their length (mean absolute value of internal angle for all sites 9°). At the heels there was greater variability in the data for both laminar orientation and internal angle. Overall, the foal feet showed greater mediolateral symmetry and less proximodistal variation than did the adult feet. In both age groups, rapid spatial changes in laminar morphology were closely associated with the position of the margins of the third phalanx.