Evaluation of changes in architecture of the stratum internum of the hoof wall from fetal, newborn, and yearling horses

OBJECTIVE: To evaluate morphologic changes of the stratum internum of hooves from near-term fetal, newborn, and yearling horses. ANIMALS: Feet from 27 near-term equine fetuses, 19 newborn foals, and 8 yearlings. PROCEDURES: Primary epidermal laminae (PEL) of the stratum internum were examined for evidence of architectural changes. RESULTS: In near-term fetuses, the PEL had a homogeneous appearance and symmetric distribution around the hoof wall with no significant differences in PEL density between the toe and quarters. However after birth, branched laminae at the toe formed within the first few weeks, which significantly increased PEL density at the toe, compared with the quarters. In yearlings, morphology of the PEL differed from that in younger foals and the PEL density was significantly greater at the toe than the quarters. The PEL density at the toe and medial and lateral quarters was significantly different from each other, as these PEL densities appeared to have been associated with conformation. No significant differences in PEL densities between forefeet and hind feet were detected in any group. CONCLUSIONS AND CLINICAL RELEVANCE: Findings indicate that the stratum internum of the inner hoof wall undergoes several morphologic changes shortly after birth. The PEL become branched with a greater PEL density at the toe than the quarters. In an asymmetric foot, more PEL were associated with the sloping side than the steep side of the foot. Findings suggested that PEL growth may also occur by bifurcation as well as by mitosis from the coronet and that wall stress may be associated with increased PEL density.