Objective: To validate an equine inertial measurement unit (IMU) system rigidly attached to a hoof against a 3-D optical kinematics system in horses during walking and trotting. Animals: 5 clinically normal horses. Procedures: 5 swing phases of the hooves of the right forelimb and hind limb were collected via both 3-D optical and IMU systems from 5 horses during walking and trotting. Linear and angular positions, velocities, and accelerations were compared between the 2 systems. Results: Of the 55 variables compared between the 2 systems, 25 had high correlations (r > 0.8) and 18 had moderate correlations (r > 0.5). Root mean squared errors were lowest in the sagittal plane and orientation (1.1 to 4.4 cm over a range of 1.5 to 1.9 m in the cranial-caudal direction and 2.5° to 3.5° over a range of 88° to 110° rotating around the medial-lateral axis). There were more differences between the 2 systems during small changes in motion, such as in the medial-lateral and proximal-distal directions and in the angular measures around the cranial-caudal and proximal-distal axes. Conclusions and Clinical Relevance: The equine IMU system may be appropriate for rigid attachment to a hoof of a horse and use in examination of linear and angular motion in the sagittal plane of the hoof during the swing phase while walking and trotting. Although promising in many respects, the IMU system cannot currently be considered clinically useful for lameness evaluation because of limitations in accuracy, attachment method, and lack of stance phase evaluation.

Objective: To examine the distribution of water in hoof wall specimens of horses via nuclear magnetic resonance (NMR) microscopy and determine changes in water distribution during hydration. Sample: 4 hoof wall specimens (2 obtained from the dorsum and 1 each obtained from the lateral quarter and lateral heel regions) of the stratum medium of healthy hooves of 1 horse. Procedures: Equine hoof wall specimens were examined via NMR microscopy. Proton density–weighted 3-D images were acquired. Changes during water absorption were assessed on sequential images. Results: The inner zone of the stratum medium had higher signals than did the outer zone. Areas of high signal intensity were evident in transverse images; these corresponded to the distribution of horn tubules. During water absorption, the increase in signal intensity started at the bottom of a specimen and extended to the upper region; it maintained the localization pattern observed before hydration. The relationship between the local maximal signals in areas corresponding to the horn tubules and minimal signal intensities in areas corresponding to the intertubular horn was similar and maintained approximately a linear distribution. Conclusions and Clinical Relevance: Based on the premise that signal intensity reflects water content, hydration in the equine hoof wall during water absorption occurred concurrently in the tubules and intertubular horn, and there was maintenance of the original water gradients. This technique can be applied for the assessment of pathophysiologic changes in the hoof wall on the basis of its hydration properties.

Objective: To investigate forelimb hoof wall strains and shape changes in unshod horses undergoing regular moderate exercise on a treadmill at selected speeds and gaits. Animals: 6 horses of various body types. Procedures: Each horse was exercised on a treadmill (walking, trotting, and cantering, with or without galloping at 12.5 m/s) 3 times a week for 4 consecutive weeks; duration of each exercise session ranged from 10 to 14 minutes. During the 4-week period, the proximal hoof circumference (PHC) and toe angle (TA) of each forelimb hoof were measured weekly with a flexible measuring tape and a hoof gauge, respectively. Forelimb hoof wall strains were measured bilaterally at the toe and each quarter (3 strain gauges) immediately before the first and after the last exercise session. Results: Strain measurements revealed a consistent pattern of deformation of the hoof wall in both forelimbs at all gaits; strains increased during the stance phase of the stride. Strain values were dependent on site and gait. Compared with initial findings, mean TA increased significantly, whereas mean PHC did not, after the 4-week exercise period. A relationship between TA changes and hoof wall strains could not be established. Conclusions and Clinical Relevance: In unshod horses, forelimb hoof wall strains were affected by site and gait, but not by discrete changes in TA; PHC did not change in response to moderate regular exercise. The pattern of hoof loading was consistent despite significant changes in TA.

Objective: To determine whether increased gene expression of a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) in laminae of horses with starch gruel–induced laminitis was accompanied by increased enzyme activity and substrate degradation. Sample: Laminae from the forelimb hooves of 8 healthy horses and 17 horses with starch gruel–induced laminitis (6 at onset of fever, 6 at onset of Obel grade 1 lameness, and 5 at onset of Obel grade 3 lameness). Procedures: Gene expression was determined by use of cDNA and real-time quantitative PCR assay. Protein expression and processing were determined via SDS-PAGE and quantitative western blotting. Protein distribution and abundance were determined via quantitative immunofluorescent staining. Results: ADAMTS-4 gene expression was increased and that of versican decreased in laminitic laminae, compared with expression in healthy laminae. Catalytically active ADAMTS-4 also was increased in the tissue, as were ADAMTS-4–cleavage fragments of versican. Immunofluorescent analyses indicated that versican was depleted from the basal epithelia of laminae of horses at onset of Obel grade 3 lameness, compared with results for healthy laminae, and this was accompanied by regional separation of basal epithelial cells from the basement membrane. Aggrecan gene and protein expression were not significantly affected. Conclusions and Clinical Relevance: Changes in gene and protein expression of ADAMTS-4 and versican in the basal epithelium of laminitic laminae indicated a fundamental change in the physiology of basal epithelial cells. This was accompanied by and may have caused detachment of these cells from the basement membrane.

Objective: To determine the expression and distribution of a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4), its substrates aggrecan and versican, and their binding partner hyaluronan in laminae of healthy horses. Sample: Laminae from the forelimb hooves of 8 healthy horses. Procedures: Real-time quantitative PCR assay was used for gene expression analysis. Hyaluronidase, chondroitinase, and keratanase digestion of lamina extracts combined with SDS-PAGE and western blotting were used for protein and proteoglycan analysis. Immunofluorescent and immunohistochemical staining of tissue sections were used for protein and hyaluronan localization. Results: Genes encoding ADAMTS-4, aggrecan, versican, and hyaluronan synthase II were expressed in laminae. The ADAMTS-4 was predominantly evident as a 51-kDa protein bearing a catalytic site neoepitope indicative of active enzyme and in situ activity, which was confirmed by the presence of aggrecan and versican fragments bearing ADAMTS-4 cleavage neoepitopes in laminar protein extracts. Aggrecan, versican, and hyaluronan were localized to basal epithelial cells within the secondary epidermal laminae. The ADAMTS-4 localized to these cells but was also present in some cells in the dermal laminae. Conclusions and Clinical Relevance: Within digital laminae, versican exclusively and aggrecan primarily localized within basal epithelial cells and both were constitutively cleaved by ADAMTS-4, which therefore contributed to their turnover. On the basis of known properties of these proteoglycans, it is possible that they can protect the basal epithelial cells of horses from biomechanical and concussive stress.