Morphological evaluation of Merkel cells and small lamellated sensory receptors in the equine foot.

OBJECTIVE To examine the equine foot for the presence of sensory receptors including Merkel cells and small lamellated Pacinian-like corpuscles (SLPCs). SAMPLE Forefeet obtained from 7 horses following euthanasia for reasons other than foot disease. PROCEDURES Disarticulated feet were cut into either sagittal sections or cross sections and immersed in neutral-buffered 4% formalin. Following fixation, samples were obtained from the midline of the dorsal aspect of the hoof wall and from the frog (cuneus ungulae) between the apex and central sulcus. The formalin-fixed, paraffin-embedded hoof wall and frog sections were routinely processed for peroxidase immunohistochemistry and stained with H&E, Alcian blue, and Masson trichrome stains for histologic evaluation. RESULTS Sensory myelinated nerves and specific receptors were identified within the epidermal and dermal tissues of the equine foot including the hoof wall laminae, coronet, and frog. Merkel cells were identified with specific antisera to villin, cytokeratin 20, and protein gene product 9.5 in coronet epidermis and hoof wall. These cells were interspersed among basilar keratinocytes within the frog, coronary epidermis, and secondary epidermal laminae. The SLPCs were present within the superficial dermis associated with the central ridge of the frog (ie, frog stay). Numerous S100 protein and protein gene product 9.5 immunoreactive sensory nerves in close proximity to these receptors were present throughout the dermal tissues within both the frog and hoof wall. CONCLUSIONS AND CLINICAL RELEVANCE The presence of Merkel cells and SLPCs that are known to detect tactile and vibrational stimuli, respectively, further defined the diverse range of neural elements within the equine foot.

Equine hoof wall tubule density and morphology.

Density and morphologic features of hoof wall tubules in horses' hooves are described. The sample population consisted of hooves (n=12) from both live and deceased adult horses. Full wall thicknesses of the hoof wall were prepared histologically from sites at the toe, medial quarter and lateral quarter. In defined areas, tubules were counted, and density was calculated across the three histologically defined areas of the stratum externum, stratum medium and stratum internum along with the descriptive morphologic features of the tubules. Morphologically, distinct zones were demarcated by varying tubular cortical and medullary characteristics. Tubule density showed a radially increasing pattern across the wall thickness. Significant regional differences in density were found in the toe, lateral and medial walls. These findings represent a first study of regional differences of tubular densities. Hoof horn clippings from live feet may have potential diagnostic and/or prognostic value.

Acupuncture Points of the Horse's Distal Thoracic Limb: A Neuroanatomic Approach to the Transposition of Traditional Points.

Veterinary acupuncture charts were developed based on the concept of transpositional points whereby human acupuncture maps were adapted to animal anatomy. Transpositional acupuncture points have traditionally been placed in specific locations around the horse's coronet and distal limb believed to be the closest approximation to the human distal limb points. Because the horse has a single digit and lacks several structures analogous to the human hand and foot, precisely transposing all of the human digital points is not anatomically possible. To date there is no published research on the effect of acupuncture treatment of the equine distal limb points. This paper presents a modified approach to equine distal limb point selection based on what is known from research on other species about the neuroanatomic method of acupuncture. A rationale is presented for modification of traditional equine ting points as well as additional points around the hoof and distal limb that do not appear in the standard textbooks of equine acupuncture. The anatomy and physiology of the equine foot likely to be affected by acupuncture are briefly reviewed. Modified neuroanatomic points are proposed that may be more accurate as transpositional points. As an example of clinical application, a neuroanatomic approach to acupuncture treatment of equine laminitis is presented.

Density and morphologic features of primary epidermal laminae in the feet of three-year-old racing Quarter Horses.

OBJECTIVE: To quantify the density of primary epidermal laminae (PELs) around the solar circumference and evaluate the relationship between regional PEL density and hoof capsule morphology in horses. SAMPLE POPULATION: Forefeet from nine 3-year-old Quarter Horse cadavers. PROCEDURES: Data pertaining to gross features of hoof morphology and PEL variables, including number, density, and distribution patterns around the perimeter of the hoof wall and number of bar PELs, were collected. Tissues of the laminar junction were examined histologically. RESULTS: No significant differences were found between left and right forefeet with respect to gross hoof morphologic measurements. Mean +/- SD number of PELs, including those at the bars of the hoof, was 551 +/- 30. Primary epidermal laminar density in the toe was significantly higher, compared with that in the quarter and heel regions, and was higher on the lateral aspect of the foot, compared with the medial aspect. Feet were significantly wider on the lateral aspect of the foot, compared with the medial aspect, as measured across the widest point of the solar surface. Histologic examination revealed atypical laminar morphology at the toe. CONCLUSIONS AND CLINICAL RELEVANCE: Variations were detected in PEL density and morphology around the solar circumference of hooves from 3-year-old racing Quarter Horses. A better understanding of relationships between laminar density, laminar morphology, and gross morphology of the hoof capsule in different populations of horses may aid practitioners in diagnosis and treatment of disease involving the hoof wall in horses.