Morphology of the Laminar Junction in Relation to the Shape of the Hoof Capsule and Distal Phalanx in Adult Horses <i>(Equus caballus)</i>

Abstract

The purpose was to investigate whether differences in equine hoof shape, which are inferred to alter foot function, are accompanied by differences in morphology of the laminar junction. Ten fore feet from adult horses were segregated into normal and low-angle groups, depending on the dorsal angle of the hoof wall. Twenty measurements of external hoof shape and four of the enclosed distal phalanx were tested for differences between groups, and for intragroup correlations. Three measurements of laminar morphology (spacing, orientation and degree of bend) were recorded for samples of up to 50 primary epidermal laminae at each of 20 sample sites. Sites were distributed over the foot in 5 circumferential columns and 4 proximodistal rows. Intergroup differences were investigated, as were correlations among sample sites of the laminar variables with the shape measurements. Results show differences in hoof shape between groups (but not bone shape) and laminar morphology. Six shape measurements are significantly different between groups: dorsal angle, medial and lateral angles, lateral sole width, solar circumference, and dorsal length. In the normal group, shape measurements show patterns of correlation among regions of the hoof, and between hoof and bone measurements. In the low-angle group, shape correlations occur largely within one region of the hoof (the heels) and in the bone measurements. Laminar spacing tends to be nonsignificantly greater in the low-angle group, while variances for laminar spacing and orientation are significantly greater in this group. Laminar spacing correlates with bone width and coronary circumference (CC) of the hoof in the normal group, but only with CC in the low-angle group. When taken as a whole, and interpreted in light of a model of foot mechanical function, the results appear to indicate a deterioration in structural coherence of the foot in the low-angle group.

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.…”

“…Previous work has shown direct correlations between external shape and laminar structure (as in Fig. 4), but the distribution of clusters was difficult to interpret (Thomason et al, 2001). The clusters implied that change in each external shape variable had an effect on a specific region of the laminar junction.…”

“…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.…”

“…It is also important to the equine industry because of its susceptibility to a disease called laminitis, which has numerous causes and can have debilitating effects on the animal (Pollitt, 1998). It is of particular interest to us because there are strong indications that it remodels in response to time-dependent variation in loading (Thomason et al, 2001;Bowker, 2003a).…”