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

Abstract

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.

Mechanical behavior and quantitative morphology of the equine laminar junction

“…2). This morphological variation is consistent with hypotheses of regional loading variability (Douglas and Thomason, 2000;Thomason, et al, 2001) as follows. At the toe, the distal phalanx is thought to pull the laminae down and back, exerting tension on the laminar junction in radial and vertical directions.…”

“…By inference, capsule shape should also affect the distribution of stress and strain magnitudes in the laminar junction and in turn affect laminar morphology. Preliminary evidence is available for this three-way interaction between mechanical behavior and the two intrinsic modifiers, in that there are patterns of correlation between measurements of external hoof shape and those of laminar morphology (Douglas and Thomason, 2000;Thomason et al, 2001). In these two studies, capsule shape was quantified by 20 external measurements, based on a list in Kane et al (1998), and including toe angle (TA; measured between the wall and ground surfaces at the toe in lateral view).…”

“…As in previous work (Douglas and Thomason, 2000;Thomason et al, 2001), the morphology of samples of PEL was quantified as LS, LO, and IA (a measure of curvature). The previous works had a small sample size (n ϭ 5) in each of two comparison groups.…”

“…Departure of laminar orientation from being perpendicular to the wall (as at the toe) and increased degrees of curvature were qualitatively reconciled with this perceived difference in mechanical behavior. At the distal margin of the distal phalanx, there are rapid deviations in spacing, orientation, and curvature, which were rationalized as being the effects of loss of physical support as the laminae migrate off the end of the bone (Douglas et al, 2000). Based on these prior inferences, the lack of significant correlation between any aspect of mechanical behavior and laminar orientation and internal angle is unexpected.…”

Density of primary and secondary epidermal laminae of equine hoof

“…Contrastingly, our results showed that both in forelimbs ( Fig.2A) and hindlimbs (Fig.2B), the region of the hoof toe had a greater concentration of primary epidermal laminae, corroborating the studies of Bowker (2003), Bidwell & Bolker (2006) Lancaster et al (2007) and Thomason et al (2008). Douglas & Thomason (2000) mentioned that the hoof toe is the region with the highest stress between the hoof wall and the distal phalanx, the gradual reduction in density of primary epidermal laminae towards the hoof bulb, as observed in the present study, probably is an adaptive response to different stresses in the several regions, once under physiological situations the force imposed in the quarters region would be lower than required in the hoof toe, as well as the stress related to the hoof bulbs is lower than to the quarters.…”