Mid-metacarpal Deep Digital Flexor Tenotomy in the Management of Refractory Laminitis in Horses

Deep digital flexor tendon transection at the mid-metacarpus was performed in 20 horses with severe acute or chronic laminitis that was not responsive to conventional treatment. Sixteen horses improved within 72 hours, one horse worsened, and two horses were unaffected by the surgery. Eleven horses survived less than 1 month after surgery and six horses survived longer than 6 months. Three horses surviving longer than 6 months have remained lame and no horse has returned to athletic performance. Transection of the deep digital flexor tendon at the mid-metacarpus may decrease the pain associated with the acute refractory stage of laminitis and may be useful as an immediate salvage procedure; however, despite the early clinical improvement observed after tenotomy, the survival rate of affected horses may not be altered.     

Clinical Updates I—Laminitis

Managing laminitis entails a multifaceted approach and includes nutritional management in all cases. Using advanced imaging techniques, as part of the diagnostic workup, provides guidance in the treatment options and includes computed tomography, computer modeling, digital radiography and venography. The therapeutic procedures are trimming, shoeing, deep flexor tenotomy and hoof wall resection as possible considerations and is dependent on the clinical findings. When applicable, preventive measures such as cryotherapy and techniques to prevent support limb laminitis can be implemented.     

Deep digital flexor tenotomy as a treatment for chronic laminitis in horses: 35 cases (1988-1997)

OBJECTIVE: To determine long-term prognosis for horses with laminitis treated by deep digital flexor (DDF) tenotomy and to identify factors affecting success of the surgical procedure. DESIGN: Retrospective study. ANIMALS: 35 horses with laminitis treated by DDF tenotomy between 1988 and 1997. PROCEDURE: Information was obtained from individual medical records and follow-up telephone interviews with owners and referring veterinarians. Cumulative proportions of horses that survived 6 months and 2 years after tenotomy were determined. Effect of Obel grade of lameness on 6-month and 2-year survival and effect of distal phalangeal rotation on survival and future performance were evaluated by chi 2 analysis. Body weights of horses that survived > or = 2 years were compared with those of horses that survived < 2 years by ANOVA. RESULTS: 27 of the 35 (77%) horses survived > or = 6 months, and 19 of 32 (59%) survived > 2 years. Obel grade of lameness and body weight at time of surgery had no effect on 6-month or 2-year survival. Degree of distal phalangeal rotation had no effect on 2-year survival or the ability of horses to be used for light riding. Twenty-two of the 30 (73%) owners interviewed indicated they would have the procedure repeated on their horses given similar circumstances. CLINICAL IMPLICATIONS: DDF tenotomy is a viable alternative for horses with laminitis refractory to conventional medical treatment. In some instances, the procedure may be effective in returning horses to light athletic use.     

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.     

Acquired flexural deformity of the distalinterphalangeal joint in horses: Treatment by desmotomy of the accessory ligament of the deep digital flexor tendon: A retrospective study

Hospital records of 29 horses treated by desmotomy ofthe accessory ligament of the deep digital flexor tendon for correction of acquired flexural deformity of the distal interphalangeal joint in one or both forelimbs were reviewed and evaluated retrospectively. Information on correction of the deformity, cosmetic appearance of the surgery site, and current use of the horses was obtained by interviews with the owners.At the time of surgery, 27 horses were less than one year old and two horses were more than one year old. Eleven months to five years after surgery, 26 horses had normal appearance of the hoof and limb, and 26 horses had acceptable cosmetic appearance of the surgery site due to no or minimal scarring. At the time of interview, all but two of the 11 horses more than three years old were in full training.It is concluded that desmotomy of the accessory ligament of the deep digital flexor tendon is an effective and cosmetically acceptable treatment for acquired flexural deformity of the distal interphalangeal joint in the horse.     

Accuracy of open magnetic resonance imaging for guiding injection of the equine deep digital flexor tendon within the hoof

Lesions of the distal deep digital flexor tendon (DDFT) are frequently diagnosed using MRI in horses with foot pain. Intralesional injection of biologic therapeutics shows promise in tendon healing; however, accurate injection of distal deep digital flexor tendon lesions within the hoof is difficult. The aim of this experimental study was to evaluate accuracy of a technique for injection of the deep digital flexor tendon within the hoof using MRI‐guidance, which could be performed in standing patients. We hypothesized that injection of the distal deep digital flexor tendon within the hoof could be accurately guided using open low‐field MRI to target either the lateral or medial lobe at a specific location. Ten cadaver limbs were positioned in an open, low‐field MRI unit. Each distal deep digital flexor tendon lobe was assigned to have a proximal (adjacent to the proximal aspect of the navicular bursa) or distal (adjacent to the navicular bone) injection. A titanium needle was inserted into each tendon lobe, guided by T1‐weighted transverse images acquired simultaneously during injection. Colored dye was injected as a marker and postinjection MRI and gross sections were assessed. The success of injection as evaluated on gross section was 85% (70% proximal, 100% distal). The success of injection as evaluated by MRI was 65% (60% proximal, 70% distal). There was no significant difference between the success of injecting the medial versus lateral lobe. The major limitation of this study was the use of cadaver limbs with normal tendons. The authors conclude that injection of the distal deep digital flexor tendon within the hoof is possible using MRI guidance.     

Laminitis in Horses: Through the Lens of Systems Theory

Systems theory is a way of describing complex and dynamic relationships. We applied systems theory to the structure and function of the equine foot in an effort to better understand laminitis and, in so doing, reconcile the various theories of its etiopathogenesis and find more universally effective preventive and therapeutic strategies. The foot is described as an open system, and its inherent vulnerabilities are explored. Cascade failure is discussed as a potentially unifying theory of laminitis. The fundamental failure in laminitis is failure of the lamellar dermal−epidermal bond, but that endpoint can be reached via vascular, enzymatic, inflammatory, or mechanical mechanisms, or any combination thereof. Inflammation is discussed as a common denominator, making anti-inflammatory therapy of greater importance than just pain management. Multimodal anti-inflammatory therapy is discussed, including selective COX-2 inhibitors, heparin, nutraceuticals, and inhibitors of matrix metalloproteinases (MMPs). Multimodal analgesic therapy also is important and may include nonsteroidal anti-inflammatory drugs (NSAIDs), opiates, epidural analgesics, physical therapy, relief of weight bearing, diligent nursing care, deep digital flexor tenotomy, and case-appropriate trimming and shoeing. Preventing laminitis still comes down to risk management: knowing the risk factors applicable to an individual horse and adjusting the management accordingly. Examples include weight management and control of carbohydrate intake in overweight horses and ponies, the use of pergolide in patients with pituitary pars intermedia dysfunction (PPID), and distal limb cryotherapy in high-risk patients. It is anticipated that application of molecular biologic techniques will further advance treatment and prevention of laminitis.     

Breakover of the hoof and its effect on stuctures and forces within the foot

The location of the breakover of the hoof capsule can be positioned through shoe placement, shoe shape, or trimming on barefoot horses. Placing the breakover in relation to the tip of PIII is a more dependable location than placing breakover guided only by visual evaluation of the hoof capsule. The hoof-pastern axis and the position of the navicular bone will be affected by the distance from the apex of the frog to breakover. The resulting decrease in strain of the deep digital flexor tendon while standing and during movement will decrease inflammation and disease in the equine digit.     

Hoof growth between two shoeing sessions leads to a substantial increase of the moment about the distal, but not the proximal, interphalangeal joint

REASONS FOR PERFORMING STUDY: There is little insight into the effects of routine farriery on the internal structures of the distal limb in sound horses. OBJECTIVES: To measure the effect of change in hoof conformation during a shoeing interval on the moments about the proximal and distal interphalangeal joints (PIPJ, DIPJ) and to determine whether and how the horse compensates for this change in hoof conformation. METHODS: Both front feet of 9 sound Warmblood horses were measured while standing on a pressure-force measuring system and radiographed in a lateromedial direction shortly after shoeing and 8 weeks later. From these data, ground reaction forces (GRF) and lever arms were measured in order to calculate joint moments. RESULTS: After 8 weeks, the moment about the PIPJ did not increase significantly, but the moment about the DIPJ did so, indicating a compensatory mechanism for a change in hoof conformation in the DIPJ. CONCLUSIONS: Standing horses compensate for hoof conformation change during an 8-week shoeing interval, which leads to increased DIPJ extension and consequently an increased loading of the deep digital flexor tendon. POTENTIAL RELEVANCE: This study quantifies the effect of a shoeing interval on the internal structures of the foot and helps to determine an appropriate shoeing interval for individual horses in which the hoof with the lowest hoof angle is the best indicator. The exact determination of an optimal individual shoeing interval requires further study.     

Correlation of Plasma Insulin Concentration with Laminitis Score in a Field Study of Equine Cushing's Disease and Equine Metabolic Syndrome

This study aimed to investigate endocrinologic test values and the response to treatment of two commonly encountered causes of endocrinopathic laminitis, equine Cushing's disease (ECD) and equine metabolic syndrome (EMS), in a veterinary practice setting. In particular, the study aimed to determine whether insulin concentration correlated to the severity of clinical laminitis in horses with EMS or ECD. Twenty-five horses were included in the study and assigned to one of three groups: ECD (n = 6), EMS (n = 10), and controls (n = 9). Blood samples were collected at an initial visit and then at regular intervals for the next 12 months. Plasma concentrations of adrenocorticotropin (ACTH), cortisol, and insulin and serum concentrations of glucose and total thyroxine (T4) were obtained. Horses with ECD had significantly higher plasma ACTH concentrations than EMS horses or controls. Horses with EMS and ECD both had significantly higher plasma insulin concentrations than control horses, which was correlated with the Obel grade of laminitis (r = 0.63). After treatment, there was a trend for a reduction in plasma ACTH concentration in horses with ECD. A program of diet and exercise for horses with EMS resulted in reductions in both plasma insulin concentrations and bodyweight, which was variable, depending on the individual. There was a significant correlation between the change in plasma insulin concentration and Obel grade of laminitis (r = 0.69). This study has highlighted the importance of baseline plasma insulin concentration as a potential indicator of the susceptibility of horses to laminitis and the response to a program of diet and exercise.     

Assessment of the ultrasonographic characteristics of the podotrochlear apparatus in clinically normal horses and horses with navicular syndrome

OBJECTIVE: To characterize the normal ultrasonographic appearance of the podotrochlear apparatus in horses by use of standardized measurements and identify soft tissue changes associated with navicular syndrome. DESIGN: Prospective study. ANIMALS: 7 clinically normal horses and 28 horses with navicular syndrome. PROCEDURE: The feasibility of identifying and measuring the soft tissue structures of the podotrochlear apparatus ultrasonographically via the transcuneal approach was assessed in 2 additional horses without navicular syndrome; both horses were euthanatized, and the structures identified ultrasonographically were confirmed at necropsy. Ultrasonographs were obtained in the study horses. Objective and subjective data were obtained to characterize ultrasonographic changes associated with navicular syndrome. RESULTS: Abnormalities of the flexor surface of the distal sesamoid (navicular) bone, the impar ligament, the distal digital annular ligament, deep digital flexor tendon (DDFT), and the podotrochlear (navicular) bursa were assessed via the transcuneal ultrasonographic approach. No significant differences were found between the measurements of the podotrochlear apparatus in normal horses and those with navicular syndrome; however, important subjective differences were detected ultrasonographically in horses with navicular syndrome. In horses with navicular syndrome, ultrasonographic findings were indicative of navicular bursitis, dystrophic mineralization of the DDFT and impar ligament, tendonitis and insertional tenopathy of the DDFT, desmitis of the impar ligament, and cortical changes in the flexor surface of the navicular bone. CONCLUSIONS AND CLINICAL RELEVANCE: Findings of ultrasonographic evaluation of the hoof appear to be useful in determining the cause of caudal heel pain and characterizing the components of navicular syndrome in horses.     

Relationship of foot conformation and force applied to the navicular bone of sound horses at the trot

REASONS FOR PERFORMING STUDY: Collapsed heels conformation has been implicated as causing radical biomechanical alterations, predisposing horses to navicular disease. However, the correlation between hoof conformation and the forces exerted on the navicular bone has not been documented. HYPOTHESIS: The angle of the distal phalanx in relation to the ground is correlated to the degree of heel collapse and foot conformation is correlated to the compressive force exerted by the deep digital flexor tendon on the navicular bone. METHODS: Thirty-one shod Irish Draught-cross type horses in routine work and farriery care were trotted over a forceplate, with 3-dimensional (3D) motion analysis system. A lateromedial radiograph of the right fore foot was obtained for each horse, and various measurements taken. Correlation coefficients were determined between hoof conformation measurements and between each of these and the force parameters at the beginning (15%) of stance phase, the middle of stance (50%) and at the beginning of breakover (86% of stance phase). Significance was defined as P<0.05. RESULTS: The force exerted on the navicular bone was negatively correlated (P<0.05) to the angle of the distal phalanx to the ground and to the ratio between heel and toe height. This was attributed to a smaller extending moment at the distal interphalangeal joint. There was not a significant correlation between the angle of the distal phalanx and the degree of heel collapse, and heel collapse was not significantly correlated to any of the force parameters. CONCLUSIONS: Hoof conformation has a marked correlation to the forces applied to the equine foot. Heel collapse, as defined by the change in heel angle in relation to toe angle, appears to be an inaccurate parameter. The forces applied on the foot are well correlated to the changes in the ratio of heel to toe heights and the angles of the distal phalanx. POTENTIAL RELEVANCE: Assessment of hoof conformation should be judged based on these parameters, as they may have clinical significance, whereas parallelism of the heel and toe is of less importance.     

Use of magnetic resonance imaging to diagnose distal sesamoid bone injury in a horse

CASE DESCRIPTION: A 5-year-old Appaloosa mare was examined for severe left forelimb lameness of 4 months' duration. CLINICAL FINDINGS: Lameness was evident at the walk and trot and was exacerbated when the horse circled to the left. Signs of pain were elicited in response to hoof testers placed over the frog of the left front hoof, and a palmar digital nerve block eliminated the lameness. Radiographs revealed no abnormalities, but magnetic resonance imaging (MRI) revealed increased bone density in the medullary cavity of the distal sesamoid (navicular) bone in the proton density and T2-weighted images and a defect in the fibrocartilage and subchondral bone of the flexor cortex. TREATMENT AND OUTCOME: Because of the absence of improvement after 4 months and the poor prognosis for return to soundness, the mare was euthanatized. An adhesion between the deep digital flexor tendon and the flexor cortex defect on the navicular bone was grossly evident, and histologic evaluation revealed diffuse replacement of marrow trabecular bone with compact lamellar bone. Changes were consistent with blunt traumatic injury to the navicular bone that resulted in bone proliferation in the medullary cavity. CLINICAL RELEVANCE: Use of MRI enabled detection of changes that were not radiographically evident and enabled accurate diagnosis of the cause of lameness. Navicular bone injury may occur without fracture and should be considered as a differential diagnosis in horses with an acute onset of severe unilateral forelimb lameness originating from the heel portion of the foot.     

In vitro reactivity of digital arteries and veins to vasoconstrictive mediators in healthy horses and in horses with early laminitis

The in vitro reactivity of vasoconstrictive mediators that are implicated in acute laminitis was determined in palmar and plantar digital arteries and veins obtained from healthy horses and in palmar digital vessels of horses with early laminitis (Obel grade I). To obtain baseline reactivity data, 3 experiments were conducted, using healthy horses: (1) the reactivity of palmar and plantar digital arteries and veins to angiotensin II, norepinephrine, and 5-hydroxytryptamine (serotonin) were compared; (2) the direct effects of bacterial endotoxin on vascular reactivity were assessed; and (3) the reactivity of palmar digital arteries and veins to angiotensin II, norepinephrine, prostaglandin F2 alpha (PGF2 alpha), serotonin, and a thromboxane-endoperoxide analog (U46619) were determined. The vascular reactivity of these same 5 vasoconstrictors then was determined in horses with early laminitis and was compared with data from healthy (control) horses. Obel grade-I laminitis was experimentally induced in horses, using carbohydrate overload. Dose responses were conducted for each agent at concentrations between 10(-8)M and 10(-4)M. The potency of a drug was defined as the mean effective concentration necessary to induce 50% of maximal contraction (EC50). There were no differences in EC50 concentrations and in maximal contractions between forelimb and hind limb arteries and veins for angiotensin II, norepinephrine, and serotonin. Incubation with endotoxin had no effect on the reactivity of arteries and veins to angiotensin II, norepinephrine, and serotonin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic changes in circulating leukocytes during the induction of equine laminitis with black walnut extract

Administration of black walnut heartwood extract (BWHE) via nasogastric tube induces acute laminitis in horses. However, the processes responsible for the development of laminitis, including laminitis induced with BWHE, remain unclear. The results of recent studies indicate that administration of BWHE initiates an inflammatory response in the laminar tissues and that this response may be due to extravasation of activated leukocytes from the circulation. This study examines the effects of BWHE administration on the dynamics of circulating neutrophils and monocytes, and the capacity of blood leukocytes to produce radical oxygen species (ROS) over the time period from administration of BWHE to the development of lameness consistent with Obel grade I laminitis.

Individual horses, free of pre-existing musculoskeletal disease, were administered either 6 l of BWHE or an equal volume of water at time 0 (T = 0). Blood samples were collected prior to dosing and at 1, 2, 3, 4, 6, 8, 10 and 12 h after dosing, or until the onset of Obel grade I laminitis. For each sample, total leukocyte counts were determined followed by collection of buffy coats and removal of erythrocytes by hypotonic lysis. Leukocytes were either fixed for flow cytometric assessment of differential counts or maintained in culture to measure endogenous and phorbol ester-induced production of ROS. At each sample time, the number of cells recovered and the flow cytometric differential counts were compared with corresponding total leukocyte counts determined by the Clinical Pathology laboratory.

Horses administered BWHE had a significant reduction in circulating leukocytes at 3–4 h relative to values for horses administered the same volume of water. Horses that developed Obel grade I laminitis had a significant reduction in circulating leukocytes when compared to values for horses administered BWHE that did not become lame. Flow cytometric analysis revealed a consistent decrease in the total number of monocytes obtained from horses that developed laminitis. In these same horses, the endogenous level of ROS production was significantly higher at T = 0 than for horses that did not become lame. Furthermore, production of ROS by leukocytes from horses that developed laminitis increased significantly and coincided with the decrease in circulating leukocytes.

Collectively, these findings support a role for systemic activation of leukocytes and induction of inflammation by BWHE as a factor in the early pathogenesis of acute laminitis. Because laminitis often develops as a sequel to diseases characterized by systemic inflammatory events, activation and emigration of neutrophils and monocytes may be important factors in the early pathogenesis of laminitis in clinical cases.     

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.     

Nuclear Factor-κB Inhibitor as a Preventive Factor of Digital Hypothermia Induced by Lipopolysaccharide in Horses

Although the mechanism of development of equine laminitis is unclear, involvement of endotoxemia has been proposed. Endotoxemia is one of the described pathways for laminitis but not the only one. Lipopolysaccharide (LPS) promotes the release of vasoconstrictors from platelets and endothelium through the activation of nuclear factor (NF)-κB in these cells. The vasoconstrictors induced by LPS may cause digital hypothermia with vasoconstriction and local ischemia, contributing to the development of laminitis. In the present study, we evaluated beneficial effect of NF-κB inhibition on digital hypothermia induced by LPS in adult horses. To generate a model for the local ischemia below the pastern, LPS was infused to the palmar lateral digital vein. As an index of blood circulation, hoof wall surface temperature (HWST) was measured. LPS infusion reduced HWST time dependently; however, the reduction of HWST was significantly prevented by pretreatment of a NF-κB inhibitor, IMD-0354. Our results clearly demonstrated that the inhibition of NF-κB prevented the digital hypothermia induced by LPS, suggesting that the NF-κB inhibitor might have a therapeutic effect on laminitis associated with endotoxemic conditions in horses.     

Treatment of acute laminitis. Supportive therapy.

Over the last decade, both the farriery and veterinary professions have greatly increased their collective experience and understanding of the treatment of acute laminitis. Many horses that would have not been considered candidates for treatment 10 to 15 years ago are now saved, and some progress to successful careers as athletes. Unfortunately, the difficulties over prediction of the course of the disease persist, which continues to complicate treatment decisions. By its nature, supportive therapy is designed to make the horse more comfortable and limit further laminar injury by countering adverse biomechanical forces. Therefore, the success of treatment depends on the degree of instability between the distal phalanx and the hoof when treatment is started as well as the effectiveness of medical and supportive therapy.     

Glucocorticoids and laminitis in the horse.

The administration of exogenously administered GCs and syndromes associated with GC excess are both attended by increased risk for the development of laminitis in adult horses. However, there exists substantial controversy as to whether excess GCs cause laminitis de novo. If true, the pathogenesis of laminitis arising from the effects of GC excess is probably different from that associated with diseases of the gastrointestinal tract and endotoxemia. Although a satisfactory explanation for the development of laminitis as a consequence of GC action is currently lacking, numerous possible and plausible theoretical mechanisms do exist. Veterinarians must exert caution with respect to the use of GCs in adult horses. The extent to which individual horses are predisposed to laminitis as a result of GC effect cannot be predicted based on current information. However, the administration of systemic GCs to horses that have been previously affected by laminitis should be used only with extreme caution, and should be accompanied by careful monitoring for further signs of laminitis. The risk of laminitis appears to be greater during treatment using some GCs (especially dexamethasone and triamcinalone) compared with others (prednisone and prednisolone). Whenever possible, to reduce the risk of laminitis, GCs should be administered locally. For example, the risk of GC-associated laminitis is evidently considerably reduced in horses affected with chronic obstructive pulmonary disease (COPD) if GC treatment is administered via inhalation. We have hypothesized that structural changes in the equine hoof that resemble laminitis may arise as a consequence of excess GC effect. Although these changes are not painful per se, and are not associated with inflammation, they could likely predispose affected horses to the development of bona fide laminitis for other reasons. Moreover, the gross morphological appearance of the chronically GC-affected hoof resembles that of a chronically foundered hoof in some respects. Further investigation into the effect of GC on the hoof lamellar interface is clearly needed.