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.     

Field study of the prevalence of lameness in horses with back problems

A population of 805 horses (70 per cent dressage, 20 per cent show jumpers and 10 per cent trotters) with orthopaedic problems was examined for signs of lameness and back problems, irrespective of their original complaints. In the horses with a back problem the prevalence of lameness was 74 per cent, and back problems were diagnosed in 32 per cent of the lame horses. These percentages were significantly higher than those recorded in a control population of 399 horses, of which 20 per cent were lame and 12 per cent had back problems. In the group of horses with orthopaedic problems there was a strong association between lameness and back problems and, in particular, there was a high prevalence of lameness among the horses with back problems.     

Effectiveness of a unique dihydropyridine (BAYTG 1000) for prevention of laminitis in horses

OBJECTIVE: To determine whether a unique dihydropyridine (BAYTG 1000) would be beneficial in preventing laminitis in horses. ANIMALS: 16 clinically normal adult horses. PROCEDURE: 8 pairs of horses were used in a controlled double-blind study, using sex- and age-matched horses randomly assigned to treatment or control groups. Horses were subjected to carbohydrate overload to induce laminitis. Treated horses were administered BAY TG 1000 (30 mg/kg, PO, q 24 h) for 3 days. Hoof wall surface temperature (HWST) and lameness were recorded at 4-hour intervals. The HWST was adjusted on the basis of time of onset of lameness and evaluated, using a repeated-measures ANOVA. Lameness 8 hours after onset and clinical status 72 hours after onset of lameness were evaluated, using Mann-Whitney procedures. RESULTS: Analysis revealed that BAYTG 1000 did not decrease the incidence of lameness but significantly ameliorated prodromal hypothermia, lessened the severity of lameness 8 hours after onset of lameness, and improved the clinical status of horses 72 hours after onset of lameness. CONCLUSION AND CLINICAL RELEVANCE: Results support the conclusion that BAYTG 1000 was protective when used in prevention of laminitis. The drug decreased severity and improved clinical status (recovery) of induced lameness, which was interpreted to mean that the drug's actions were on mechanisms important but secondary to primary causal mechanisms of laminitis. Therefore, drugs that enhance digital perfusion via alteration of rheologic activity may have potential use in the prevention and management of laminitis in horses.     

DOPPLER MEASUREMENT OF SPLANCHNIC BLOOD FLOW DURING DIGESTION IN UNSEDATED NORMAL DOGS

The purpose of this study was to measure splanchnic blood flow during digestion in unsedated dogs by using duplex Doppler sonography. The study population consisted of 12 healthy dogs. Blood flow in the cranial mesenteric artery, the celiac artery, and the aorta was measured before a test meal and at 20, 60, and 90 minutes after eating. The following measurements were made or calculated: vessel diameter, peak systolic velocity, end diastolic velocity, mean velocity, resistive index, pulsatility index, and flow volume. There was a significant postprandial decrease in the resistive and pulsatility indices in both the cranial mesenteric (preprandial RI = 0.867, postprandial RI = 0.796, preprandial PI = 3.033, postprandial PI = 2.173) and the celiac (preprandial RI = 0.854, postprandial RI = 0.769, preprandial PI = 2.639, postprandial PI = 1.930) arteries. In both vessels the end diastolic velocity, the mean velocity, and the flow volume increased significantly postprandially. These changes occurred significantly earlier in the celiac artery than in the cranial mesenteric artery. The findings most likely correspond to postprandial splanchnic vasodilation. Doppler ultrasound provide a good methode of detecting changes in postprandial splanchnic blood flow in the dog.     

Submural histopathologic changes attributable to peracute laminitis in horses

OBJECTIVE: To describe submural histopathologic changes attributable to peracute laminitis in horses. ANIMALS: 20 adult horses. PROCEDURE: A concurrent-control design was used to compare laminar lesions in 10 horses subjected to carbohydrate-induced laminitis with laminar characteristics of 10 sex- and aged-matched control horses with normal feet. Horses in the treatment group were administered an overload of carbohydrate. Tissues were obtained by biopsy 4 to 8 hours after onset of lameness or 72 hours after administration of the carbohydrate overload when lameness did not develop. Sections were stained with H&E, Masson's trichrome, and periodic acid-Schiff stains. Histopathologic changes were analyzed to detect differences between groups and to correlate epidermal changes with severity and duration of lameness. RESULTS: Analysis indicated that dermal and epidermal lesions were evident despite lack of visible separation of the epidermal basement membrane, can be found in horses without detectable lameness, and were nonspecific and progressive following onset of lameness. Furthermore, severity and location of lesions were associated with severity and duration of lameness. CONCLUSION AND CLINICAL RELEVANCE: These observations are consistent with the concept that separation of the laminar epithelial basement membrane is a delayed step in the pathogenesis of acute laminitis, digital vascular hypoperfusion is an underlying cause for laminitis, and the potential for repeated episodes of subclinical laminitis may underlie the development of structural and mechanical changes consistent with chronic laminitis despite lack of clinical signs of acute laminitis.     

Effects of topical nitroglycerine patches and ointment on digital venous plasma nitric oxide concentrations and digital blood flow in healthy conscious horses

OBJECTIVE: To measure and compare palmar digital venous plasma nitric oxide (NO) concentrations and digital arterial blood flow after application of topical nitroglycerine (NTG). STUDY DESIGN: Experimental study. ANIMALS: Healthy adult horses (n=8). METHODS: Digital blood flow was measured by an ultrasonic Doppler flow probe surgically implanted around the medial palmar digital artery. Blood was collected from a catheter placed in the medial palmar digital vein for quantification of NO. NTG patches, NTG ointment or control patches were placed over the palmar digital vessels at the level of the fetlock. Two horses had an intra-arterial infusion of an NTG solution into the medial palmar digital artery in a pilot study. RESULTS: Digital arterial blood flow did not change significantly with application of the NTG patches, NTG ointment, or control patches. There were no statistically significant or biologically important changes in digital venous NO concentrations across time or between treated and control horses. In the pilot study, digital arterial blood flow and palmar digital venous NO concentrations increased with intra-arterial infusion of NTG. CONCLUSIONS: In clinically healthy horses, digital arterial blood flow and digital venous plasma NO concentrations did not change significantly with application of the NTG patches/ointment. These treatments are unlikely to have an effect on the digital vasculature of laminitic horses, however, further investigation is warranted. CLINICAL RELEVANCE: Although NTG patches have been used as a method of decreasing vasomotor tone and improving digital blood flow in horses with laminitis, this study provides evidence in healthy conscious horses that this treatment is not effective in altering digital blood flow.     

B‐mode and power Doppler ultrasonography of the equine suspensory ligament branches: A descriptive study on 13 horses

Ultrasonography is routinely used to achieve the diagnosis of equine suspensory ligament desmopathy. In human medicine, power Doppler ultrasonography has also been found to be useful for the diagnosis of tendon/ligament injuries. The aim of this prospective, pilot study was to assess the presence or absence of power Doppler signal in suspensory ligament branches and compare B‐mode findings with power Doppler findings in suspensory ligament branches of lame and non‐lame limbs. Thirteen horses were used (eight lame horses, with lameness related to pain in the suspensory ligament branches, and five non‐lame horses). Ten lame limbs and 24 sound limbs were assessed by B‐mode and power Doppler ultrasonography. The severity of power Doppler signal was scored by two independent readers. The B‐mode ultrasonographic examination revealed abnormalities in branches of lame limbs and in branches of sound limbs. Suspensory ligament branches that were considered normal in B‐mode showed no power Doppler signal. However, power Doppler signal was detected in suspensory ligament branches that were abnormal in B‐mode, both in lame and sound limbs. Power Doppler scores were subjectively higher in suspensory ligament branches of lame limbs and in branches with more severe B‐mode changes. Findings supported the use of power Doppler as an adjunctive diagnostic test for lame horses with suspected suspensory desmopathy.     

Assessing the Association Between Hoof Thermography and Hoof Doppler Ultrasonography for the Diagnosis of Lameness in Horses

The objectives of this study were to assess the correlation between hoof surface temperature and ultrasonographic measurements of digital blood vessels in horses and to evaluate the measurements' potential as predictors for clinical lameness. Twelve 3-year-old American Quarter Horses, 6 geldings and 6 mares, with average initial body weight of 459 ± 31 kg were used. On days 0, 30, 60, and 90 of the study, horses were weighed and subjected to clinical lameness examinations. Doppler ultrasonography was used to measure diameter of the medial palmar artery in the distal left forelimb and velocity of blood flow through that artery, starting at 60 minutes after morning feeding and repeated at 30-minute intervals. Temperature measurements on the hoof were collected at 15-minute intervals beginning 75 minutes after feeding, using a digital thermographic camera. A series of bivariate linear mixed models were fitted to estimate the correlation between Doppler and temperature measurements. The within-horse and between-horse correlations between hoof surface temperature and velocity of blood flow in the distal limb through the medial palmar artery was estimated at 0.40 (P > .50) and 0.99 (P < .001), respectively. These results indicate that at the horse level, the correlation between hoof temperature and velocity of blood flow in the distal limb was very high but that the within-horse correlation was not significantly different from 0. Velocity of blood flow at 60 minutes after feeding improved model fit to the lameness data, so it was included as a model predictor for lameness.     

Voluntary limb-load distribution in horses with acute and chronic laminitis

OBJECTIVES: To compare limb-load distribution between horses with and without acute or chronic laminitis. ANIMALS: 10 horses with carbohydrate-induced acute laminitis, 20 horses with naturally occurring chronic laminitis, and 20 horses without foot abnormalities (controls). PROCEDURES: Limb-load distribution was determined, using a custom-designed system that allowed simultaneous quantification of the mean percentage of body weight voluntarily placed on each limb (ie, mean limb load) and the SD of the mean load over a 5-minute period (ie, load distribution profile [LDP]). Load distribution profile was used as an index of frequency of load redistribution. RESULTS: Mean loads on fore- and hind limbs in control horses were 58 and 42%, respectively, and loads were equally and normally distributed between left and right limbs. In addition, forelimb LDP was greater, compared with hind limbs, and was affected by head and neck movement. In comparison, limb-load distribution in horses with chronic laminitis was characterized by an increase in the preferential loading of a forelimb, a decrease in total forelimb load, and an increase in LDP that was correlated with severity of lameness. In horses with carbohydrate-induced acute laminitis, mean limb loads after onset of lameness were not different from those prior to lameness; however, LDP was significantly decreased after onset of lameness. CONCLUSION AND CLINICAL RELEVANCE: Quantification of limb-load distribution may be an applicable screening method for detecting acute laminitis, grading severity of lameness, and monitoring rehabilitation of horses with chronic laminitis.     

Comparison of milk yield in dairy cows with different degrees of lameness

OBJECTIVE: To compare milk yield among cows classified as nonlame, moderately lame, and lame and to examine the relationship between severity of lameness and milk yield in cows classified as lame during the first 100 days after parturition. DESIGN: Longitudinal study. ANIMALS: 465 Holstein cows. PROCEDURE: Cows were examined weekly during the first 100 days after parturition and assigned a lameness score by use of a 6-point locomotion scoring system (ie, 0 to 5). Milk yield was compared among cows classified as nonlame, moderately lame, and lame. Among cows classified as lame (locomotion score > or = 4), milk yield was compared for cows with low, medium, and high cumulative locomotion scores. Cows classified as lame were further examined on a tilt table for diagnosis and treatment of lameness. RESULTS: 84 (18%), 212 (46%), and 169 (36%) cows were classified as nonlame, moderately lame, and lame, respectively. Among cows in their second or later lactations, milk yield in lame cows was significantly lower than that in moderately lame and nonlame cows. In addition, among cows classified as lame, milk yield was significantly lower in cows with high locomotion scores during the first 100 days after parturition, compared with cows with low scores. Most (58%) cows classified as lame had laminitis. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate a linear relationship between increasing degree of lameness and decreasing milk yield among cows in their second or later lactations. The locomotion scoring system used in this study may be a useful management tool that veterinarians and dairy farmers could adopt for early detection of lameness in dairy cows.     

SCINTIGRAPHIC ASSESSMENT OF THE METACARPOPHALANGEAL AND METATARSOPHALANGEAL JOINTS OF HORSES WITH JOINT PAIN

Our aims were to evaluate the pattern of radiopharmaceutical uptake in horses with lameness related to the metacarpophalangeal and/or metatarsophalangeal joint and compare the results with similar information from sound horses. It was hypothesized that there would be a difference in radiopharmaceutical uptake between the lame and contralateral limb in unilaterally lame horses and that there would be a difference between lame and sound horses. Nuclear scintigraphic images of 43 horses with forelimb lameness and 30 horses with hindlimb lameness were evaluated. In all horses lameness was improved by intraarticular analgesia of the joint, or by perineural analgesia of the palmar/plantar (at the junction of the proximal 3/4 and the distal 1/4 of the metacarpal/metatarsal regions) and palmar/plantar metacarpal/metatarsal nerves. All images were assessed subjectively and a quantitative image analysis was performed by drawing a vertical line profile through the center of each joint in the lateral images and using region of interest analysis in both lateral and dorsal/plantar images. Ratios of radiopharmaceutical uptake were compared for each region between lame and contralateral limbs in unilaterally lame horses and between lame and control horses. There was a significant difference in the ratio of radiopharmaceutical uptake in the proximal aspect of the proximal phalanx between lame and nonlame forelimbs in unilaterally lame horses and in both lame and contralateral limbs of lame horses compared with control horses for the regions of the distal aspect of the third metacarpal/metatarsal bone and the proximal sesamoid bones. However, the profile analysis was of limited clinical value.     

The relationship between serum biotin and oxidant/antioxidant activities in bovine lameness

Serum biotin concentrations, erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), reduced glutathione (GSH) and plasma thiobarbituric acid reactive substances (TBARS) were measured in 36 dairy cows, 18 of them were healthy and served as control. In the 18 cows with lameness problems, there were 5 cows with interdigital necrobacillosis, 5 cows with subsolar abscessation, 2 cows with solar ulcers, 2 cows with white line disease, 2 cows with chronic laminitis and 2 cows with septic arthritis. The degree of lameness was estimated to be slight in 3 cows, moderate in 11 cows and severe in 4 cows. Plasma fibrinogen levels and TBARS concentrations were increased significantly (P≤0.05) in lame cows compared to control group. The antioxidant enzymes GSH-Px, and CAT concentrations were increased significantly (P≤0.05) in lame cows. The level of reduced glutathione and the activity of SOD were significantly decreased in affected cows compared to healthy ones. Serum biotin levels in healthy cows ranged from 2.25 to 3.5ng/ml while in lame cows, biotin levels ranged from 1.17 to 2.3ng/ml. Biotin levels correlated positively with blood GSH (r=0.870, P≤0.05), (r=0.735, P≤0.05) and with GSH-Px (r=0.539, P≤0.05), (r=0.637, P≤0.05) and with SOD (r=0.637, P≤0.05), (r=0.449, P≤0.05) and with catalase (r=0.533, P≤0.05), (r=0.585, P≤0.05) in both healthy and lameness affected subjects, respectively.     

Comparison of the Sedative and Hemodynamic Effects of Acepromazine and Promethazine in the Standing Horse

The objective of this study was to compare the sedative and peripheral hemodynamic effects of acepromazine (ACP) and promethazine (PTZ) in the standing healthy horse. Nine healthy Warmblood horses randomly received either intravenous ACP at 0.1 mg/kg or PTZ at 0.1, 0.2, and 0.3 mg/kg. A sedation score based on clinical examination was recorded, and systolic arterial blood pressure was noninvasively evaluated using a Doppler flow detector at the tail, just before and every 15 minutes until 60 minutes after drug injection. Hemodynamics of the median artery of the left forelimb was studied using Doppler ultrasonography just before and 45 minutes after injection of the drug, which allowed calculation of surface (SURF), diameter (DIAM), and circumference (CIRC) of the vessel and peak systolic velocity (PSV), end diastolic velocity (EDV), mean velocity (MV), volumetric flow (VF), and resistivity index (RI) of the blood flow. Regardless of the dose used, PTZ had lesser sedative and hypotensive effects than ACP at 0.1 mg/kg and did not induce significant variations in SURF, DIAM, CIRC, PSV, EDV, MV, VF, and RI of the studied standing horses. Conversely, the vasodilatory properties of ACP were illustrated by a significant increase in SURF, DIAM, CIRC, PSV, EDV, MV, and VF and a significant reduction of the RI. Unlike ACP, PTZ did not induce alterations on the morphology of the Doppler waveform. PTZ appears to have less sedative and peripheral vasodilator effects than ACP, thus it could be safer than ACP in patients suffering from hypotension.     

Equine laminitis model: Cryotherapy reduces the severity of lesions evaluated seven days after induction with oligofructose

Reasons for performing study: A previous preliminary study demonstrated the potential of distal limb cryotherapy (DLC) for preventing laminitis. Clinically, DLC must be effective for periods longer than 48 h and the preventive effect must extend beyond its discontinuation. Objectives: To evaluate the effect of DLC, applied during the developmental phase of induced laminitis, on the severity of clinical laminitis and lamellar histopathology 7 days after dosing. Methods: Eighteen normal Standardbred horses were divided into 3 groups of 6. Continuous cryotherapy was applied for 72 h to the distal limbs of the first group. The second and third groups were administered laminitis inducing doses of oligofructose and 72 h of cryotherapy applied (immediately after dosing) to the second group. After clinical assessment all horses were subjected to euthanasia 7 days after dosing and hoof lamellar tissues were harvested and analysed. Results: In the laminitis induced horses clinical lameness and laminitis histopathology was significantly reduced in horses that underwent 72 h of DLC compared with untreated controls. Cryotherapy alone produced no significant lameness or other ill effect. Conclusions: Continuous, medium‐ to long‐term (72 h) cryotherapy applied to the distal limbs of horses safely and effectively ameliorates the clinical signs and pathology of acute laminitis. Potential relevance: Pre‐emptive distal limb cryotherapy is a practical method of ameliorating laminitis in ill horses at risk of developing the disease.     

Inflammatory Cytokine Gene Expression in Blood During the Development of Oligofructose-Induced Laminitis in Horses

Systemic inflammation is a risk factor for laminitis in horses and precedes the onset of lameness in experimental models. We therefore hypothesized that whole-blood inflammatory cytokine expression would increase during the development of laminitis in a carbohydrate overload model. Blood samples were obtained from 14 horses undergoing laminitis induction with 10 g/kg oligofructose as part of another study. Samples were collected at 0, 8, 12, 16, 20, and 24 hours, and lameness evaluations were performed every 4 hours. Expression levels of interleukin-1β (IL-1β), IL-6, IL-8, IL-10, and tumor necrosis factor-α were measured in whole blood by using real-time PCR. IL-1β, IL-8, and IL-10 expression increased above baseline from 8 to 24 hours (P < .001), and IL-6 expression increased at 16 and 20 hours (P = .005). Expression of tumor necrosis factor-α did not change over time. All horses developed clinical laminitis between 12 and 24 hours. Increased mean IL-1β, IL-8, and IL-10 expression detected at 8 hours therefore preceded the onset of lameness. We conclude that peripheral leukocyte cytokine expression increases as systemic inflammation develops in an alimentary carbohydrate overload model of laminitis, and this precedes detection of lameness. Results support current recommendations to control the systemic inflammatory response in order to lower the risk of laminitis in horses.     

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.     

Closed Suction Drainage in the Treatment of Infectious Arthritis of the Equine Tarsocrural Joint

Infectious arthritis of the tarsocrural joint was treated in 13 horses with closed suction drainage through a flat, fenestrated, latex (Jackson-Pratt) drain, broad-spectrum antimicrobial agents, nonsteroidal anti-inflammatory drugs, and bandage immobilization. In 11 horses, arthroscopic lavage and debridement were also performed. Ingress drains were placed for lavage in six horses. Ten horses returned to their previous level of competition or were sound. One horse raced but had lameness of the affected tarsocrural joint and dropped in racing class; one horse was euthanatized because of laminitis in the supporting limb; and one horse was lame, but useful as a breeding animal. Closed suction drainage appeared to be a useful treatment in horses with infectious arthritis. Although arthroscopy was not necessary, it facilitated fibrin removal, lavage, and partial synovectomy. Because of the development of Pseudomonas superinfection in one horse, the use of simultaneous ingress catheters was not recommended.     

Risk factors for development of acute laminitis in horses during hospitalization: 73 cases (1997-2004)

OBJECTIVE: To identify risk factors for development of acute laminitis in horses during hospitalization for illness or injury. DESIGN: Retrospective case-control study. ANIMALS: 73 horses that developed laminitis (case horses) and 146 horses that did not develop laminitis (control horses) during hospitalization. PROCEDURES: Case and control horses were matched in a 2:1 ratio by the date on which each horse was evaluated. Potential risk factors investigated included age, breed, and sex; highest and lowest values recorded during hospitalization for fibrinogen concentration, WBC count, PCV, and total solids concentration; and comorbid disease states, including pneumonia, endotoxemia, diarrhea, medically treated colic, surgically treated colic, pituitary adenoma, retained placenta or metritis, forelimb lameness, hind limb lameness, acute renal failure, and vascular abnormalities. A univariate screening of all potential risk factors was performed to determine which variables should be selected for further analysis. All factors found to be associated with development of laminitis were included in a multivariate conditional logistic regression model. RESULTS: Development of laminitis was marginally associated with lowest and highest fibrinogen concentrations, highest PCV, and lowest total solids concentration and significantly associated with pneumonia, endotoxemia, diarrhea, abdominal surgery for colic, and vascular abnormalities. In the multivariate analysis, only endotoxemia was significantly associated with laminitis. CONCLUSIONS AND CLINICAL RELEVANCE: Endotoxemia is an important risk factor for development of acute laminitis in horses during hospitalization for medical or surgical conditions. Early recognition of endotoxemia, or the potential for it to develop in certain disease states, and initiation of treatment directed at endotoxemia or its consequences may help prevent laminitis in horses during hospitalization.     

Lameness and heart rate elevation in the exercising horse

Seven, healthy, conditioned, Quarter Horse mares with previous treadmill experience were each fitted with an adjustable heart bar shoe on the left front foot and a counterbalanced bar shoe on the right front foot. Three treatments were studied: sound, slightly lame, and obviously lame at a trot. Each subject performed one standardized exercise test (SET) daily on three consecutive days. Each subject underwent one treatment during a SET. Treatment order was randomly assigned. The SET consisted of a 5-rain exercise period at 3.2 m/sec on a treadmill at an 11% grade. Heart rate (HR) was determined at rest, 20 rain after the induction of lameness before the SET, during the last 30 sec of the SET, and at 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, and 60 min postexercise. The Student's paired t test was used to compare HR means for the three treatments at each monitoring interval. Heart rate was higher in slightly lame trials compared to sound trials as rest and at 0.5 through 10 and 30 through 60 min postexercise (P<0.05 to P<0.001). Lame trials evidenced higher HRs than slightly lame trials at rest and at 0.5, 2, 4, and 5 rain of recovery (P<0.05). When lame HRs were compared to sound HRs, differences were noted at rest and at 0.5 through 60 min postexercise (P<0.01 to P<0.001). The heart bar shoe as designed for the treatment of laminitis was effective as a noninvasive, nonpermanent model of lameness pain in normal horses. Increases in HR at rest and during recovery from exercise were observed with experimentally induced lameness. The degree of HR increase seen with lameness was a function of the degree of lameness induced.     

Equine laminitis: Induced by 48 h hyperinsulinaemia in Standardbred horses

Reasons for performing study: Hyperinsulinaemia is known to induce laminitis experimentally in healthy ponies with no history of the condition. Horses are more insulin sensitive than ponies and whether prolonged hyperinsulinaemia and euglycaemia would have a similar laminitogenic effect requires study. Objectives: To determine if laminitis results when the prolonged euglycaemic hyperinsulinaemic clamp technique (p‐EHC) is applied to clinically normal Standardbred horses, and to monitor hoof wall temperature seeking an association between vascular activity and laminitis development. Methods: Eight young, clinically normal Standardbred horses were assigned into 4 pairs and within each pair, one was assigned randomly to either treatment (n = 4) or control (n = 4) groups. Treated horses received continuous infusions of insulin and glucose until clinical signs of laminitis developed, at which point the horses were subjected to euthanasia. Control horses received an equivalent volume of a balanced electrolyte infusion for the same period. Hoof wall surface temperature (HWST) was monitored continuously throughout the experimental period. Results: All horses in the treatment group were calculated to have normal insulin sensitivity. All treated horses, and none in the control group, developed laminitis (P = 0.01). Pronounced digital pulses were a feature of the treatment group, while insignificant digital pulses occurred in control horses. HWST was higher and less variable in treated horses once hyperinsulinaemia was established. Conclusions: Healthy Standardbred horses subjected to prolonged hyperinsulinaemia develop laminitis within 48 h, demonstrating that laminitis in horses can be triggered by insulin. Potential relevance: Insulin resistance and the associated hyperinsulinaemia place horses and ponies at risk of developing laminitis. This study demonstrates a need for prompt management of the persistent hyperinsulinaemia seen in some endocrinopathies.