MAGNETIC RESONANCE IMAGING OF THE EQUINE DIGIT WITH CHRONIC LAMINITIS

Chronic laminitis is a severe disease affecting the equine digit. It was hypothesized that magnetic resonance (MR) imaging would improve visualization of structures within the foot and pathology associated with chronic laminitis. This study aimed to describe the MR imaging findings in chronic laminitis, compare different pulse sequences for visualization of pathology, and to compare MR imaging with standard radiography. Twenty (10 forelimb, 10 hindlimb) cadaver limbs from 10 horses clinically diagnosed with chronic laminitis (group L) and 10 limbs without laminitis (group N) were used. Lateromedial radiographs and sagittal and transverse MR images of the foot were obtained. Radiographs and MR images were evaluated for anatomic definition and evidence of pathology. Dorsal hoof wall thickness and angle of rotation and displacement distance of the distal phalanx were measured. Comparisons were made between group L and N, forelimb and hindlimb within each horse, and MR imaging and radiography. Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically.     

Treatment of solar prolapse using the heart bar shoe and dorsal hoof wall resection technique

This paper describes the treatment of 10 horses suffering from acute laminitis using the heart bar shoe and a dorsal hoof wall resection technique. All cases had progressed to prolapse of the tip of the pedal bone covered by solar corium through the horny sole; in one case the exposed tip of the distal phalanx became visible. Nine cases of distal phalangeal rotation and one case of distal displacement of the distal phalanx (sinking) are described. Two animals were destroyed because of the degree of lameness, one remains slightly lame at the trot and the remaining seven have returned to their previous use at comparable levels of performance.     

A Novel Approach to the Treatment and Prevention of Laminitis: Botulinum Toxin Type A for the Treatment of Laminitis

Laminitis is an inflammation of the lamina of hoofed animals. According to the United States Department of Agriculture (USDA), laminitis impacts approximately 2% of the horse population each year. Because of the severity of the inflammation and chronic pain, it is frequently necessary to euthanize these horses. Surviving horses may be left useless, with resultant economic and social impact on the industry. Current interventions for laminitis are based on supportive care and alteration of biomechanical forces on the digit. The transition from laminitis to laminar failure (founder) is believed to be caused by the “weight of the horse and the forces of locomotion driving the bone down into the hoof capsule.” We hypothesize that an important factor is the torsional forces placed on the distal phalanx (coffin bone) by the deep digital flexor muscle and tendon. The paralyzing effect of botulinum toxin will result in a decrease of these torsional forces and therefore will aid in the prevention or treatment of the sequelae of laminitis. Seven horses with varying degrees of laminitis were evaluated. Each underwent pretreatment and posttreatment radiographs as well as pretreatment and posttreatment Obel grading. Each horse received botulinum toxin type A injected into the belly of the deep digital flexor muscle. In all cases there was radiographic stabilization of pedal displacement from the dorsal hoof wall. Obel scores showed improvement of 1 to 2 grades during the time monitored.     

Equine laminitis model: Lamellar histopathology seven days after induction with oligofructose

Reasons for performing study: The histopathology of laminitis during its transition from the acute to the chronic phase has not been previously documented. Studying hoof lamellar tissues 7 days after induction of laminitis may provide insight into the intractable nature of the chronic phase of the disease. Objectives: To induce laminitis and investigate hoof wall lamellar tissues 7 days after dosing. Methods: Laminitis was induced using oligofructose in 6 normal Standardbred horses. The dorsal hoof lamellar tissues of these and 12 normal horses were processed and examined by light microscopy. Serial sections of a lamellar tip affected by laminitis were used to create a 3 dimensional reconstruction. Results: Transverse sections of dorsal hoof wall lamellae were significantly longer than normal. Many secondary epidermal lamellae were not connected to primary lamellae and existed as spherical or ovoid, discrete islands isolated in the lamellar dermis. The lamellar basement membrane was intact. Conclusions: Lamellar tissue has the ability to reorganise rapidly following an episode of acute laminitis. Although histopathological evidence of ongoing acute laminitis was absent by 7 days, there was marked disruption of lamellar architecture. Potential relevance: The architecture and subsequent strength of the resultant lamellar interface could be greatly influenced for the better by strategies that minimise mechanical displacement during the acute phase of laminitis.     

The Effect of Oral Isoxsuprine and Pentoxifylline on Digital and Laminar Blood Flow in Healthy Horses

OBJECTIVE: To quantitate blood flow in the palmar digital artery and dorsal laminae of the hoof in standing, unmedicated, nonsedated horses, and in horses treated with oral isoxsuprine, oral pentoxifylline, and intravenous acetylpromazine as a positive control. STUDY DESIGN: Experimental study; treatments administered in a random cross-over design. ANIMALS: A total of 6 healthy horses selected with at least one nonpigmented forelimb hoof wall and determined to be free of laminitis. METHODS: All horses were instrumented with a flow probe placed around one palmar digital artery under general anesthesia and a laser doppler flow probe placed within a hole in the dorsal hoof wall to measure digital blood flow and laminar perfusion respectively. Baseline readings of palmar digital blood flow and laminar perfusion were recorded before and between treatments. Horses were randomly assigned to one of two groups and treated with either isoxsuprine (1.2 mg/kg, orally twice daily for 10 days) or pentoxifylline (4.4 mg/kg, orally every 8 hours for 10 days) in a random cross-over design. Digital blood flow (DBF) and laminar perfusion (LP) were measured on days 2, 5, 7, and 10 of treatment. Horses also received acetylpromazine as a positive control (0.066 mg/kg, intravenously) during the washout period, and measurements were taken every 15 minutes until measurements returned to baseline readings. Data were analyzed by using repeated measures ANOVA. RESULTS: Digital blood flow (11.2 to 97.7 mL/min) and laminar perfusion (1.0 to 11.1 Capillary Perfusion Units) differed between horses. No statistically significant increases in DBF or LP were detected over the 10 day treatment period with either isoxsuprine or pentoxifylline. Acepromazine resulted in a significant increase (P = .0007) in DBF for approximately 75 minutes beginning 15 minutes after treatment. A mild but insignificant increase in LP was identified after acetylpromazine treatment. CONCLUSION: Neither isoxsuprine nor pentoxifylline increased blood flow to the digit or dorsal laminae in healthy horses. Acepromazine caused an increased blood flow to the digit. Based on the results of this study acetylpromazine potentially would have a greater effect on improving digital blood flow than oral isoxsuprine or pentoxifylline when treating ischemic conditions of the foot in horses.     

Surgical reconstruction of chronic coronary band avulsions in three horses

Three adult horses were admitted with chronic coronary band avulsions of 2-, 3-, and 46-month durations, respectively. The hoof had a typical appearance in all 3 horses, with a spur of coronary band and associated horn growing at right angles to the hoof wall. Each horse was anesthetized, and the coronary band was reconstructed. Follow-up evaluation of the 3 horses (12, 15, and 23 months after surgery, respectively), revealed healing of all 3 avulsed coronary bands. Mild roughening of the hoof wall distal to the previous avulsion site was observed.     

Hindlimb laminar inflammatory response is similar to that present in forelimbs after carbohydrate overload in horses

Reasons for performing study: A significant proinflammatory response is known to occur in the forelimb lamina after carbohydrate administration. As the hindlimbs are often less affected by laminitis compared with the forelimbs, we assessed hindlimb inflammatory response in the early stages of carbohydrate‐induced laminitis to determine whether differences in the response existed. Objective: To determine whether a similar proinflammatory response occurs in the hindlimb laminae to that previously reported for the forelimb. Methods: Archived laminar samples from 12 horses administered 17.6 g of starch (85% corn starch, 15% wood flour)/kg bwt via nasogastric tube that were anaesthetised either after developing a temperature >38.9°C (DEV; n = 6) or at the onset of Obel grade 1 lameness (OG1; n = 6) were used in addition to 6 control horses (CON) that were anaesthetised 24 h after administration of water. Real‐time quantitative polymerase chain reaction for selected proinflammatory mediators and MAC387 immunohistochemistry were performed. The data were analysed nonparametrically to compare groups. Results: Increases in laminar MAC387‐positive leucocytes and laminar messenger ribonucleic acid (mRNA) concentrations (P<0.05) for interleukin‐1β, interleukin‐6, cyclo‐oxygenase‐2, chemokine (C‐X‐C motif)ligand (CXCL)1 and CXCL8 were present in both fore‐ and hindlimb laminae from horses with OG1 lameness. Both CXCL1 and CXCL8 were also increased in forelimb and hindlimb laminae in the DEV horses. Conclusions: Administration of carbohydrate resulted in a similar inflammatory response in the hindlimb laminae to that previously reported for the forelimb laminae. These findings suggest that other factors, such as weightbearing, may play an important role in the development of laminitis after a systemic inflammatory condition develops. Potential relevance: Evidence of inflammation in the hindlimb laminae suggests that the hindfeet should be addressed in the septic horse at risk for laminitis; however, laminitis is often less severe in the hindlimbs due to other factors, such as weightbearing and hoof angle.     

Gamma scintigraphic analysis of the distribution of perfusion of blood in the equine foot during black walnut (Juglans nigra)-induced laminitis

Twelve horses, with acute laminitis (primarily in the forefeet) at 12 hours after intragastric dosing with an aqueous extract of black walnut (Juglans nigra) heart-wood, were studied. The distribution of perfusion of blood to the foot and to outlined regions within the foot was quantified, using gamma scintigraphy of regionally infused 99mTc-labeled macroaggregated albumin, before and 12 hours after extract administration. Horses 1 to 3 were not studied further. Perfusion was quantified again for horses 4 to 12 at 84 hours after extract administration. At the onset of acute laminitis, horses 7 to 12 were administered a single dose of prazosin (0.025 mg/kg of body weight, IV) immediately after scintigraphy of the right forelimb and before scintigraphy of the left forelimb. When compared with baseline images, perfusion to the forefoot of horses after the development of acute laminitis was quantitatively decreased vs perfusion to the entire distal portion of the forelimb. Also with the onset of laminitis, perfusion also decreased to the dorsal laminar and coronary corium regions vs the distal portion of the forelimb. The acute laminitis-associated deficit in perfusion to the dorsal laminitis-associated deficit in perfusion deficit in perfusion to either the coronary corium or the entire forefoot. Equivalent deficits in the distribution of perfusion were not detected in forelimbs from horses with acute laminitis and which had been treated with prazosin. When compared with baseline images, perfusion to the dorsal lamina was increased in relation to perfusion to the distal portion of the limb at postdosing hour 84. Prazosin treatment did not influence that increase in perfusion to the dorsal lamina.     

Glucose transport in the equine hoof

Reasons for performing study: Several conditions associated with laminitis in horses are also associated with insulin resistance, which represents the failure of glucose uptake via the insulin‐responsive glucose transport proteins in certain tissues. Glucose starvation is a possible mechanism of laminitis, but glucose uptake mechanisms in the hoof are not well understood. Objectives: To determine whether glucose uptake in equine lamellae is dependent on insulin, to characterise the glucose transport mechanism in lamellae from healthy horses and ponies, and to compare this with ponies with laminitis. Methods: Study 1 investigated the effects of insulin (300 µU/ml; acute and 24 h) and various concentrations of glucose up to 24 mmol/l, on 2‐deoxy‐D‐[2,6‐³H]glucose uptake in hoof lamellar explants in vitro. Study 2 measured the mRNA expression of GLUT1 and GLUT4 transport proteins by PCR analysis in coronary band and lamellar tissue from healthy horses and ponies, ponies with insulin‐induced laminitis, and ponies suffering from chronic laminitis as a result of equine Cushing's syndrome. Results: Glucose uptake was not affected by insulin. Furthermore, the relationship between glucose concentration and glucose uptake was consistent with an insulin‐independent glucose transport system. GLUT1 mRNA expression was strong in brain, coronary band and lamellar tissue, but was weak in skeletal muscle. Expression of GLUT4 mRNA was strong in skeletal muscle, but was either absent or barely detectable in coronary band and lamellar tissue. Conclusions: The results do not support a glucose deprivation model for laminitis, in which glucose uptake in the hoof is impaired by reduced insulin sensitivity. Hoof lamellae rely on a GLUT1‐mediated glucose transport system, and it is unlikely that GLUT4 proteins play a substantial role in this tissue. Potential relevance: Laminitis associated with insulin resistance is unlikely to be due to impaired glucose uptake and subsequent glucose deprivation in lamellae.     

Clinical Outcome of 14 Obese,Laminitic Horses Managed with the Same Rehabilitation Protocol

A specific method of rehabilitation was used to manage obese horses with laminitis, and clinical outcome was evaluated after 5 to 20 months. Clinical data from 14 similar laminitis cases were statistically analyzed to evaluate response to rehabilitation. Data were analyzed using repeated measures or logistic regression methodologies. Each horse presented as obese and laminitic with no history of a systemic inflammatory disease. The rehabilitation method emphasized a mineral-balanced, low nonstructural carbohydrate diet; daily exercise; hoof trimming that minimized hoof wall loading; and sole protection in the form of rubber hoof boots and/or hoof casts. Distal phalanx alignment within the hoof capsule was significantly improved, and hoof wall thickness was significantly decreased (P < .0001) following treatment. Solar depth was significantly increased (P < .0015). Reduction of palmar angle measurements was detected in acutely and chronically affected horses. This treatment effect was statistically greater for horses with chronic laminitis than for horses with acute laminitis (P interaction < .0001). Horses were 5.5 times more likely to be sound post-treatment than before treatment. Daily exercise, dietary modification, and removal of ground reaction force from the hoof wall were foci of the rehabilitation program. Hoof care and husbandry as applied to these horses may be an effective method of rehabilitation of horses from obesity-associated laminitis.     

External characteristics of the lateral aspect of the hoof differ between non-lame and lame horses

During a pre-purchase examination (PPE) there is always a debate about how clinical findings of the hoof different from ideal should be interpreted in relation to future lameness risk and/or unsuitability of the horse for the potential purchaser. The objectives of this study were to describe and compare external angular measurements, linear ratios and hoof capsule characteristics of non-lame and lame feet. Photographs of feet from 300 horses with foot pain and 25 non-lame horses were analysed. Hoof wall, heel and coronary band angles and hoof wall length and height, weight-bearing length, coronary band length and height of the coronary band at dorsal and palmar locations were measured and expressed as linear ratios.Mean hoof wall, heel and coronary band angles were larger in lame compared with non-lame feet; only the ratio of dorsal to palmar coronary band heights and the shape of the coronary band were significantly different between lame and non-lame horses. Growth rings were divergent and horn tubules were non-parallel in lameness of >3 months. At a PPE, a larger ratio of dorsal to palmar coronary band heights in one limb may be indicative of previous lameness in that foot. Changes in coronary band shape and divergent growth rings and horn tubules would suggest a longer duration.     

Cytokeratins of the matrices of the chestnut (torus carpeus) and periople in horses with acute laminitis

OBJECTIVES: To determine whether there is a change in the expression of cytokeratins in the epidermal cells of the non-weight-bearing parts of the limb in horses with acute laminitis and thus determine whether the morphologic changes that develop in the periople and chestnut (torus carpeus) of horses early in acute laminitis are caused by inhibition of keratinocyte differentiation. ANIMALS: 8 horses with acute laminitis. PROCEDURE: Tissue specimens were obtained from the chestnuts of all 8 horses and from the stratum externum of the hoof wall of 3 horses. Tissue specimens were obtained within 48 hours of the first clinical signs of laminitis. The cytokeratins were characterized by 1- and 2-dimensional gel electrophoresis, and the tissue distribution of the cytokeratins was studied by immunohistochemical staining. RESULTS: The biochemical findings indicated that the epidermal cells of tissues from horses affected by laminitis contained the same set of cytokeratins as corresponding tissues from clinically normal horses. Immunohistochemistry on sections from specimens of horses with laminitis versus clinically normal horses indicated a difference in the expression of cytokeratin in the basal cells in the matrix of the stratum externum of the hoof wall and in the matrix of the chestnut of horses with laminitis in which the most severe morphologic changes were observed. CONCLUSIONS: Inhibition of keratinocyte differentiation, as observed by immunohistochemical changes, in cells in parts of the chestnut and periople may indirectly indicate that the observed epidermal changes in horses with laminitis are primary and are unaffected by weight-bearing.     

Deep digital flexor tendon force and digital mechanics in normal ponies and ponies with rotation of the distal phalanx as a sequel to laminitis

REASONS FOR PERFORMING STUDY: Previous studies have implicated tension in the deep digital flexor tendon (DDFT) in the rotation of the distal phalanx (DP) after the breakdown of the dorsal laminae caused by laminitis. Howeveer, once the DP has rotated, the DDFT should become shorter, reducing the force it exerts on the DP. OBJECTIVE: To compare DDFT force and ground reaction forces (GRFs) in normal ponies and ponies with rotation of the DP as a sequel to laminitis. METHODS: Six normal ponies (Group 1) and 6 sound ponies with 6-13 degrees of rotation of the DP in relation to the dorsal hoof wall (Group 2) were assessed at trot using forceplate and motion analysis. The force in the DDFT was calculated by assuming that the extending moment at the distal interphalangeal (DIP) joint resulting from the GRF was equal to the flexing moment created by the force in the DDFT during the stance phase (inverse dynamics). RESULTS: In early stance, the peak DDFT force (mean+/-s.d.) in the normal ponies was 1.92+/-1.63 N/kg. However, in Group 2, the point of zero moment was palmar to the centre of rotation of the DIP joint for the first 40% of stance and hence DDFT force was zero. Force in the DDFT reached a peak of 10.00+/-3.56 N/kg at 60.7+/-5.6% of stance in Group 1 and 6.41+/-1.37 N/kg at 79.2+/-9.6% of stance in Group 2. CONCLUSIONS: DDFT force in Group 2 laminitic ponies was much reduced until late stance, when it neared normal values. POTENTIAL RELEVANCE: Further studies of ponies with rotation of the DP as a sequel to laminitis should assist farriery aimed at reducing the force in the DDFT through the breakover phase of stance to protect damaged dorsal laminae.     

Decreased expression of p63, a regulator of epidermal stem cells, in the chronic laminitic equine hoof

Reasons for performing study: Abnormal epidermal stem cell regulation may contribute to the pathogenesis of equine chronic laminitis. Objective: To analyse the involvement of p63, a regulator of epidermal stem cell proliferative potential, in chronic laminitis. Methods: Epidermal tissues from skin, coronet and lamellae of the dorsal foot were harvested from 5 horses with chronic laminitis and 5 control horses. Tissues were analysed using histopathology, immunofluorescence microscopy and quantitative immunoblotting Results: Hoof lamellae of laminitic horses had a lower frequency of p63 positive cells than control lamellae, particularly in the distal region. Quantitative immunoblotting confirmed reduced p63 expression in the laminitic distal lamellar region. The decreased p63 expression in laminitic epidermal lamellae was most apparent in the abaxial region adjacent to the hoof wall and highly associated with the formation of terminally differentiated, dysplastic and hyperkeratotic epidermis in this region, whereas lamellae from control horses maintained high p63 expression throughout the axial‐abaxial axis. Conclusions: Expression of p63 in equine skin resembles that reported in other species, including man and rodents, suggesting that p63 can serve as a marker for the proliferative potential of equine epidermal stem cells. p63 expression was significantly lower in the chronic laminitic hoof than in that of control horses, suggesting laminitic hoof epithelium has more limited proliferative potential with a shift towards differentiation. This may reflect reduced activity of epidermal stem cells in laminitic hoof. It is proposed that p63 contributes to the maintenance of hoof lamellae and that misregulation of p63 expression may lead to epidermal dysplasia during lamellar wedge formation. Potential relevance: This study suggests that loss of epidermal stem cells contributes to the pathogenesis of equine laminitis. Autologous transplantation of p63‐positive epidermal stem cells from unaffected regions may have regenerative therapeutic potential for laminitic horses.     

Retrospective analysis of distal limb conformation and lameness in mature horses after desmotomy of the accessory ligament of the deep digital flexor tendon for management of a flexural deformity

Mature horses that present with flexural deformity of the distal interphalangeal joint and lameness isolated to the foot may obtain long‐term benefits from desmotomy of the accessory ligament of the deep digital flexor tendon (ALDDFT). This retrospective analysis of medical records and radiographs included 13 horses, aged ≥2 years, presented for lameness isolated to the hoof region and diagnosed with flexural deformity of the distal interphalangeal joint. Radiographic angles of the hoof and distal interphalangeal joint and lameness scores were compared before and after desmotomy of the ALDDFT. Follow‐up data including the ability to perform the intended use were obtained at least one year after surgery. There was improvement in the angle between the dorsal aspect of the third phalanx and the weightbearing surface of the hoof, improved alignment between the dorsal hoof wall and dorsal aspect of the third phalanx, and improved alignment of the distal interphalangeal joint. Lameness was decreased in 9/13 horses and 10/13 horses were performing at their level of intended use. Evidence of improved hoof conformation and lameness following desmotomy of the ALDDFT in lame horses with flexural deformity of the distal interphalangeal joint would indicate this procedure should be considered in mature horses.     

Evaluation of the Integrity of Horse Hoof Dermal and Epidermal Tissues Collected by Dorsal Transmural Access

The purpose of this study was to evaluate the integrity of dermal and epidermal tissues collected by dorsal transmural access. Eight healthy adult horses were subjected to two biopsies of the right hoof, with a 24-hour interval. To ensure hoof integrity, a radiographic evaluation with dorsopalmar and lateromedial positions was performed. The animals were sedated, and the pedal tissue was collected from two sites that were 2 cm distal to the coronary band. For each biopsy, the hoof wall was perforated using an aluminum oxide drill bit, 4.8 mm in diameter that was connected to a drilling machine, yielding a hole of approximately 9.0 mm. The perforation procedure was performed slowly in the stratum medium until 1 mm of it remained, which was determined by evaluating the movement in response to pressure applied with a Halstead forceps. Laminar deep incisions were performed with a number 11 scalpel blade until the distal phalanx was reached. The laminar tissue was then removed using a Frahm scaler. A cuboid laminar sample measuring approximately 5 mm at the base and 7 mm in height was obtained. The samples were suitable for analysis by histology and transmission electron microscopy showing that the ends of the secondary epidermal laminae were round, the basement membrane was intact between the secondary epidermal laminae and secondary dermal laminae, and the ultrastructural analysis of the cells showed their structural integrity.     

RADIOGRAPHIC APPEARANCE OF THE FEET OF MAMMOTH DONKEYS AND THE FINDING OF SUBCLINICAL LAMINITIS

All feet of 10 clinically sound mammoth donkeys (Group I) were radiographed to determine the appearance of the distal phalanx. The distal phalanges had blunted to concave-shaped dorsal solar margins which varied in appearance from slight to pronounced. The distal phalanges of the forefeet were wider than those of the hindfeet, and also were positioned a greater distance from the dorsal aspect of the hoof wall. The greater distance between the dorsal aspect of the hoof wall and the distal phalanges seemed related to the presence of a periosteal-like bony proliferation on the dorsum of the distal phalanx. This bony proliferation occurred in those distal phalanges which also had radiographic findings consistent with pedal osteitis. Next, all feet of 5 additional mammoth donkeys (Group II) that were to be necropsied for various reasons, were examined similarly to Group I, necropsied and found to have laminitis. Only 2 of these 5 donkeys had been lame; only one had rotation of the distal phalanges (in the forefeet). Radiographic data from the 4 donkeys without rotation seemed most similar to that found in those Group I donkeys which had periosteal reactions on their distal phalanges. Conclusions from this study were that: 1) feet of mammoth donkeys have some anatomic differences from those of domestic horses, 2) subclinical laminitis and pedal osteitis can occur in mammoth donkeys, 3) rotation of the distal phalanx occurs in some, but not all laminitic donkeys, 4) laminitic changes may be more pronounced in their fore than in their hindfeet, and 5) additional studies of donkeys need to be done, examining both proven normal and confirmed laminitic feet.     

Evaluation of tachykinins and their receptors to determine sensory innervation in the dorsal hoof wall and insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet of horses

OBJECTIVE: To localize substance P (SP) and neurokinin A (NKA) and their receptors in the insertion of the distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), and dorsal hoof wall of healthy feet of horses. SAMPLE POPULATION: 18 healthy feet from horses. PROCEDURE: Samples from the dorsal hoof wall and insertion of the DSIL and DDFT of 10 feet were processed for immunocytochemical analysis, using rabbit polyclonal antisera raised against SP and NKA. Tissue sections from 8 feet were incubated with 125-labeled SP to localize tachykinin receptors and their specificity and with control solutions of radioactive SP and excess nonradioactive SP to identify areas of nonspecific binding. RESULTS: Many nerves immunoreactive for SP and NKA were localized to the region of the insertion of the DSIL and DDFT and the accompanying microvasculature and arteriovenous complexes (AVC) as well as to the microvasculature of the dorsal hoof wall. Specific neurokinin 1 receptors were localized over the microvessels and AVC of the insertion zone and small microvessels of the hoof wall. CONCLUSIONS AND CLINICAL RELEVANCE: These results document that the microvasculature of the equine foot is richly innervated and has specific receptors for tachykinins. Distributions of these tachykinin receptors on the microvasculature suggest that they form an important vasodilatory mechanism for controlling blood flow through the DSILDDFT insertion and dorsal hoof wall.     

Toe white line separation associated with the notch (crena marginalis) on the distal phalanges in Thoroughbred yearling horses

The shape of the white line of the hoof is closely related to the shape of the notch on the dorsal distal bearing border of the distal phalanx (P3). In this study, a radiographic survey of the P3 of both forelimbs of 163 Thoroughbred yearling horses was conducted. The correlation of the depth and width of the notch were analyzed with the toe white line separation grades (0 to 3). As a result, the toe white line separation grade increased, the depth and the width of the notch also increased significantly. Radiographic examination of the P3 of the forelimbs might be useful for deciding whether to implement hoof care to prevent onset of toe white line separation.