Blood Glucose and Insulin Concentrations after Octreotide Administration in Horses With Insulin Dysregulation

Background

Octreotide is a somatostatin analog that suppresses insulin secretion.

Hypothesis

We hypothesized that octreotide would suppress insulin concentrations in horses and that normal (N) horses and those with insulin dysregulation (ID) would differ significantly in their plasma glucose and insulin responses to administration of octreotide.

Animals

Twelve horses, N = 5, ID = 7.

Methods

Prospective study. An oral sugar test was performed to assign horses to N and ID groups. Octreotide (1.0 μg/kg IV) was then administered, and blood was collected at 0, 5, 10, 15, 20, 25, 30, 45, 60, 75, and 90 minute, and 2, 3, 4, 6, 8, 12, and 24 hour for measurement of glucose and insulin concentrations. Area under the curve (AUC) values were calculated.

Results

Mean AUC values for glucose and insulin did not differ between normal (n = 5) and ID (n = 7) groups after octreotide injection. Significant time (P < .001) effects were detected for glucose and insulin concentrations. A group × time interaction (P = .091) was detected for insulin concentrations after administration of octreotide, but the group (P = .33) effect was not significant.

Conclusions and Clinical Importance

Octreotide suppresses insulin secretion, resulting in hyperglycemia, and then concentrations increase above baseline as glycemic control is restored. Our hypothesis that octreotide causes insulin concentrations to decrease in horses was supported, but differences between N and ID groups did not reach statistical significance when blood glucose and insulin responses were compared. The utility of an octreotide response test remains to be determined.

Pathogenesis and Treatment of Sole Ulcers and White Line Disease

Sole ulcers and white line disease are 2 of the most common claw horn lesions in confined dairy cattle. Predisposing causes include unbalanced weight bearing, and metabolic, enzymatic, and hormonal changes. The white line serves as the junction between the sole and axial and abaxial wall. It is vulnerable to trauma and separation, permitting organic matter to become entrapped. Colonization contributes to retrograde movement of the infection to the solar and perioplic corium, where an abscess forms resulting in pain and lameness. Successful treatment requires an orthopedic foot block to the healthy claw and corrective trimming of the lesion.

Evaluation of a Chemiluminescent Immunoassay for Measurement of Equine Insulin

BACKGROUND

Many diagnostic tests for insulin dysregulation use reference intervals established with an insulin radioimmunoassay (RIA) that is no longer available. A chemiluminescent immunoassay (CLIA) is commonly used for the measurement of serum insulin concentration in clinical practice but requires further validation, especially at clinically relevant reference intervals.

OBJECTIVES

To evaluate the CLIA for measurement of equine insulin and compare it to the previously validated, but now unavailable RIA.

SAMPLES

Equine serum samples (n = 78) from clinical and experimental studies.

METHODS

In this experimental study, performance of the CLIA was evaluated using standard variables, including comparison with the RIA. Continuous and binary outcomes were analyzed.

RESULTS

The CLIA showed good intra-assay (coefficient of variation [CV], 1.8-2.4%) and interassay (CV, 3-7.1%) precision. Acceptable recovery on dilution (100 ± 10%) was achieved only at dilutions <1:1. Recovery on addition was acceptable. Comparison of the CLIA and RIA showed strong positive correlation (r = 0.91-0.98), with fixed and proportional bias. At 3 diagnostic cutoffs, sensitivity of CLIA compared with RIA ranged from 67 to 100% and specificity from 96 to 100%.

CONCLUSIONS AND CLINICAL IMPORTANCE

The CLIA is a highly repeatable assay which is suitable for within- and between-horse comparisons. Dilution of high concentration samples should be performed with charcoal-stripped serum (CSS) and at the lowest dilution factor possible. At concentrations commonly used for diagnosis of insulin dysregulation (≤100 μIU/mL), results from the CLIA tend to be lower than from the RIA and should be interpreted accordingly. Further standardization of equine insulin assays is required.

Musculoskeletal Disease in Aged Horses and Its Management

Musculoskeletal disorders are the most prevalent health problem in aging horses. They are not life threatening, but are painful and an important welfare issue. Chronic joint disease (osteoarthritis) and chronic laminitis are the most prevalent. Treating osteoarthritis in the elderly horse is similar to treating performance horses, but aims at providing a stable situation with optimal comfort. Immediate medical treatment of flare-ups, long-term pain management, and adaptation of exercise and living conditions are the mainstays of treatment. Laminitis in the geriatric horse is related often to pituitary pars intermedia dysfunction, which may be treated with additional pergolide.

Disease and pharmacologic risk factors for first and subsequent episodes of equine laminitis: A cohort study of free-text electronic medical records

Electronic medical records from first opinion equine veterinary practice may represent a unique resource for epidemiologic research. The appropriateness of this resource for risk factor analyses was explored as part of an investigation into clinical and pharmacologic risk factors for laminitis. Amalgamated medical records from seven UK practices were subjected to text mining to identify laminitis episodes, systemic or intra-synovial corticosteroid prescription, diseases known to affect laminitis risk and clinical signs or syndromes likely to lead to corticosteroid use. Cox proportional hazard models and Prentice, Williams, Peterson models for repeated events were used to estimate associations with time to first, or subsequent laminitis episodes, respectively. Over seventy percent of horses that were diagnosed with laminitis suffered at least one recurrence. Risk factors for first and subsequent laminitis episodes were found to vary. Corticosteroid use (prednisolone only) was only significantly associated with subsequent, and not initial laminitis episodes. Electronic medical record use for such analyses is plausible and offers important advantages over more traditional data sources. It does, however, pose challenges and limitations that must be taken into account, and requires a conceptual change to disease diagnosis which should be considered carefully.

Effects of Common Equine Endocrine Diseases on Reproduction

Endocrine diseases, such as equine metabolic syndrome and pituitary pars intermedia dysfunction, are common in domesticated horse populations, and the frequency with which these diseases are encountered and managed by equine veterinary practitioners is expected to increase as the population ages. As clinicians learn more about the effects of these diseases on equine reproductive physiology and efficiency (including effects on reproductive seasonality, ovulation efficiency, implantation, early pregnancy loss, duration of pregnancy, and lactation), strategies and guidelines for improving fertility in affected animals continue to evolve. It is hoped that further research will establish these recommendations more firmly.

The effect of hypothermia on influx of leukocytes in the digital lamellae of horses with oligofructose-induced laminitis

Sepsis-related laminitis (SRL) is a common complication in the septic/endotoxemic critically-ill equine patient, in which lamellar injury and failure commonly lead to crippling distal displacement of the distal phalanx. Similar to organ injury in human sepsis, lamellar injury in SRL has been associated with inflammatory events, including the influx of leukocytes into the lamellar tissue and markedly increased expression of a wide array of inflammatory mediators at the onset of Obel grade 1 (OG1) laminitis. The only treatment reported both clinically and experimentally to protect the lamellae in SRL, local hypothermia ("cryotherapy"), has been demonstrated to effectively inhibit lamellar expression of multiple inflammatory mediators when initiated at the time of administration of a carbohydrate overload in experimental models of SRL. However, the effect of hypothermia on leukocyte influx into affected tissue has not been assessed. We hypothesized that cryotherapy inhibits leukocyte emigration into the digital lamellae in SRL. Immunohistochemical staining using leukocyte markers MAC387 (marker of neutrophils, activated monocytes) and CD163 (monocyte/macrophage-specific marker) was performed on archived lamellar tissue samples from an experimental model of SRL in which one forelimb was maintained at ambient temperature (AMB) and one forelimb was immersed in ice water (ICE) immediately following enteral oligofructose administration (10g/kg, n=14 horses). Lamellae were harvested at 24h post-oligofructose administration (DEV, n=7) or at the onset of OG1 laminitis (OG1, n=7). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n=10 (40× fields/digit for MAC387 and 20x fields/digit for CD163)] obtained using Aperio microscopy imaging analysis software. Data were assessed for normality and analyzed with a paired t-test and one-way ANOVA with significance set at p<0.05. MAC387-positive cells were present in low numbers in the lamellar tissue and were decreased in the hypothermic limbs (vs. AMB limbs, p<0.05) in the OG1 group; no change in CD163-positive cell numbers was noted across the conditions of the model. This study demonstrated that hypothermia of the distal limbs instituted early in the disease process in the horse at risk of SRL significantly attenuates the increase of MAC387-positive leukocytes in the digital lamellae, but has minimal effect on increases in lamellar concentrations of the major leukocyte cell type present in that tissue, CD163-positive mononuclear cells.

Prolonged hyperinsulinemia affects metabolic signal transduction markers in a tissue specific manner

Insulin dysregulation is common in horses although the mechanisms of metabolic dysfunction are poorly understood. We hypothesized that insulin signaling in striated (cardiac and skeletal) muscle and lamellae may be mediated through different receptors as a result of receptor content, and that transcriptional regulation of downstream signal transduction and glucose transport may also differ between tissues sites during hyperinsulinemia. Archived samples from horses treated with a prolonged insulin infusion or a balanced electrolyte solution were used. All treated horses developed marked hyperinsulinemia and clinical laminitis. Protein expression was compared across tissues for the insulin receptor and insulin-like growth factor 1 receptor (IGF-1R) by immunoblotting. Gene expression of metabolic insulin-signaling markers (insulin receptor substrate 1, Akt2, and glycogen synthase kinase 3 beta [GSK-3β]) and glucose transport (basal glucose transporter 1 and insulin-sensitive glucose transporter 4) was evaluated using real-time reverse transcription polymerase chain reaction. Lamellar tissue contained significantly more IGF-1R protein than skeletal muscle, indicating the potential significance of IGF-1R signaling for this tissue. Gene expression of the selected markers of insulin signaling and glucose transport in skeletal muscle and lamellar tissues was unaffected by prolonged hyperinsulinemia. In contrast, the significant upregulation of Akt2, GSK-3β, GLUT1, and GLUT4 gene expression in cardiac tissue suggested that the prolonged hyperinsulinemia induced an increase in insulin sensitivity and a transcriptional activation of glucose transport. Responses to insulin are tissue-specific, and extrapolation of data across tissue sites is inappropriate.

Evaluation of Four Diagnostic Tests for Insulin Dysregulation in Adult Light-Breed Horses

BACKGROUND

Several tests have been evaluated in horses for quantifying insulin dysregulation to support a diagnosis of equine metabolic syndrome. Comparing the performance of these tests in the same horses will provide clarification of their accuracy in the diagnosis of equine insulin dysregulation.

OBJECTIVES

The aim of this study was to evaluate the agreement between basal serum insulin concentrations (BIC), the oral sugar test (OST), the combined glucose-insulin test (CGIT), and the frequently sampled insulin-modified intravenous glucose tolerance test (FSIGTT).

ANIMALS

Twelve healthy, light-breed horses.

METHODS

Randomized, prospective study. Each of the above tests was performed on 12 horses.

RESULTS

Minimal model analysis of the FSIGTT was considered the reference standard and classified 7 horses as insulin resistant (IR) and 5 as insulin sensitive (IS). In contrast, BIC and OST assessment using conventional cut-off values classified all horses as IS. Kappa coefficients, measuring agreement among BIC, OST, CGIT, and FSIGTT were poor to fair. Sensitivity of the CGIT (positive phase duration of the glucose curve >45 minutes) was 85.7% and specificity was 40%, whereas CGIT ([insulin]45 >100 μIU/mL) sensitivity and specificity were 28.5% and 100%, respectively. Area under the glucose curve (AUCg0-120 ) was significantly correlated among the OST, CGIT, and FSIGTT, but Bland-Altman method and Lin's concordance coefficient showed a lack of agreement.

CONCLUSIONS

Current criteria for diagnosis of insulin resistance using BIC and the OST are highly specific but lack sensitivity. The CGIT displayed better sensitivity and specificity, but modifications may be necessary to improve agreement with minimal model analysis.

Decision-tree analysis of clinical data to aid diagnostic reasoning for equine laminitis: a cross-sectional study

The objective of this cross-sectional study was to compare the prevalence of selected clinical signs in laminitis cases and non-laminitic but lame controls to evaluate their capability to discriminate laminitis from other causes of lameness. Participating veterinary practitioners completed a checklist of laminitis-associated clinical signs identified by literature review. Cases were defined as horses/ponies with veterinary-diagnosed, clinically apparent laminitis; controls were horses/ponies with any lameness other than laminitis. Associations were tested by logistic regression with adjusted odds ratios (ORs) and 95% confidence intervals, with veterinary practice as an a priori fixed effect. Multivariable analysis using graphical classification tree-based statistical models linked laminitis prevalence with specific combinations of clinical signs. Data were collected for 588 cases and 201 controls. Five clinical signs had a difference in prevalence of greater than +50 per cent: 'reluctance to walk' (OR 4.4), 'short, stilted gait at walk' (OR 9.4), 'difficulty turning' (OR 16.9), 'shifting weight' (OR 17.7) and 'increased digital pulse' (OR 13.2) (all P<0.001). 'Bilateral forelimb lameness' was the best discriminator; 92 per cent of animals with this clinical sign had laminitis (OR 40.5, P<0.001). If, in addition, horses/ponies had an 'increased digital pulse', 99 per cent were identified as laminitis. 'Presence of a flat/convex sole' also significantly enhanced clinical diagnosis discrimination (OR 15.5, P<0.001). This is the first epidemiological laminitis study to use decision-tree analysis, providing the first evidence base for evaluating clinical signs to differentially diagnose laminitis from other causes of lameness. Improved evaluation of the clinical signs displayed by laminitic animals examined by first-opinion practitioners will lead to equine welfare improvements.

Oxidative stress in hoof laminar tissue of horses with lethal gastrointestinal diseases

Tissue damage caused by oxidative stress is involved in the pathogenesis of several diseases in animals and man, and is believed to play a role in the development of laminitis in horses. The aim of this study was to investigate the oxidative stress associated with laminar lesions in horses with lethal gastrointestinal disorders. Laminar tissue samples of the hoof of 30 horses were used. Tissue samples were divided as follows: six healthy horses (control group-CG), and 24 horses that died after complications of gastrointestinal diseases (group suffering from gastrointestinal disorders-GDG). Superoxide dismutase (SOD2) and nitrotyrosine immunostaining and the severity of laminar lesions were evaluated. Presence of laminar lesions and immunostaining for nitrotyrosine and SOD2 were only evident in horses from the GDG group. Thus, oxidative stress may play a role in the pathogenesis of laminar lesions secondary to gastrointestinal disorders.

Effect of increased adiposity on insulin sensitivity and adipokine concentrations in different equine breeds adapted to cereal-rich or fat-rich meals

The relationships between diet, obesity and insulin dysregulation in equids require further investigation due to their association with laminitis. This study examined the effect of dietary glycaemic load and increased adiposity on insulin sensitivity and adipokine concentrations in different equine breeds. Equal numbers of Standardbred horses, mixed-breed ponies and Andalusian horses were provided with ad libitum hay plus either cereal-rich (CHO; n = 12), fat-rich (FAT; n = 12) or control (CON; n = 9) meals over 20 weeks. The isocaloric CHO and FAT diets were fed to induce obesity by gradually increasing the supplementary feeds to provide 200% of daily digestible energy requirements by Week 20. The CON group were fed a basal ration only and maintained moderate body condition. At Week 20, the CHO and FAT groups demonstrated significantly increased body condition score, bodyweight, total body fat mass and plasma leptin concentrations compared with the CON group (P <0.001). The CHO group had lower insulin sensitivity (SI; P <0.001) and higher acute insulin response to glucose (P = 0.002) than the CON group. In contrast, the FAT group was no different to the control group. Ponies and Andalusians had lower SI values compared with Standardbreds, regardless of diet group (P = 0.001). Adiponectin concentrations were similar between the FAT and CON groups, but were significantly lower in the CHO group (P = 0.010). The provision of cereal-rich meals appeared to be a more important determinant of insulin sensitivity than the induction of obesity per se. Whether hypoadiponectinaemia is a cause or consequence of insulin dysregulation warrants further investigation.

Intraosseous infusion of the distal phalanx compared to systemic intravenous infusion for marimastat delivery to equine lamellar tissue

No validated laminitis drug therapy exists, yet pharmaceutical agents with potential for laminitis prevention have been identified. Many of these are impractical for systemic administration but may be effective if administered locally. This study compared intraosseous infusion of the distal phalanx (IOIDP) with systemic intravenous constant rate infusion (CRI) to determine which was more effective for lamellar marimastat delivery. Ultrafiltration probes were placed in both forefeet of five horses to collect lamellar interstitial fluid as lamellar ultrafiltrate (LUF). Marimastat solution (3.5 mg/mL) containing lidocaine (20 mg/mL) was infused by IOIDP at 0.15 mL/min for 12 h. After a 12 h wash-out, marimastat (3.5 mg/mL) and lidocaine were infused by constant rate infusion (CRI) at 0.15 mL/min for 12 h. LUF, plasma and lamellar tissue marimastat concentrations were quantified using UPLC-MS. Zymography was used to establish the inhibitory concentrations of marimastat for equine lamellar matrix metalloproteinases (MMPs). Data were analysed non-parametrically. There was no difference between the steady-state marimastat concentration in lamellar ultrafiltrate (LUF[M]) during IOIDP (139[88-497] ng/mL) and CRI (136[93-157] ng/mL). During IOIDP, there was no difference between marimastat concentrations in the treated foot (139[88-497] ng/mL), the untreated foot (91[63-154] ng/mL) and plasma (101[93-118] ng/mL). LUF[M] after IOIDP and CRI were >IC50 of lamellar MMP-2 and 9, but below the concentration considered necessary for in vivo laminitis prevention. Lamellar drug delivery during IOIDP was inconsistent and did not achieve higher lamellar marimastat concentrations than CRI. Modification or refinement of the IOIDP technique is necessary if it is to be consistently effective.

Musculoskeletal Pathology

The current understanding of pathology as it relates to common diseases of the equine musculoskeletal system is reviewed. Conditions are organized under the fundamental categories of developmental, exercise-induced, infectious, and miscellaneous pathology. The overview of developmental pathology incorporates the new classification system of juvenile osteochondral conditions. Discussion of exercise-induced pathology emphasizes increased understanding of the contribution of cumulative microdamage caused by repetitive cyclic loading. Miscellaneous musculoskeletal pathology focuses on laminitis, which current knowledge indicates should be regarded as a clinical syndrome with a variety of possible distinct mechanisms of structural failure that are outlined in this overview.

Investigation of single and paired measurements of adrenocorticotropic hormone for the diagnosis of pituitary pars intermedia dysfunction in horses

Background

Paired measurement of ACTH concentration may be more reliable than a single measurement.

Hypothesis/Objectives

To determine whether the mean of 2 measurements of ACTH concentration is more reliable in assessing pituitary pars intermedia dysfunction (PPID) than a single measurement.

Animals

Paired ACTH measurements were performed on (1) 148 occasions from 124 horses being investigated for PPID, (2) 90 occasions from 76 horses with PPID that were receiving treatment with pergolide, and (3) 63 occasions from 50 horses in which there was no clinical suspicion of PPID. Histologic examination of the pars intermedia was performed in 67 of the untreated horses.

Methods

Outcome of testing using single and the mean of paired samples was compared directly and both methods were compared against histology, which was considered the gold standard.

Results

Paired ACTH measurement altered binary classification as healthy or diseased in 6 of 211 cases, all off which had equivocal initial ACTH concentrations between 20 and 39 pg/mL. Using histology as the gold standard, optimal sensitivity and specificity for diagnosing PPID were 69.4 and 80.9%, respectively, for a single measurement and 72.2 and 76.2%, respectively, for paired measurements. The area under the receiver operating characteristic curve was 0.72 and 0.73 for single and paired measurements compared with histopathologic diagnosis, respectively.

Conclusions and Clinical Importance

Paired measurement of ACTH concentration offers no advantage over a single measurement.

Vasorelaxation responses to insulin in laminar vessel rings from healthy, lean horses

Hyperinsulinemia causes laminitis experimentally and is a risk factor for naturally occurring laminitis. The aim of this study was to investigate the effects of insulin on laminar vascular relaxation and to induce insulin-associated vascular dysfunction in vitro. Relaxation responses of isolated laminar arterial and venous rings to acetylcholine and insulin were evaluated. To alter vascular function in response to insulin, all vessel rings were incubated with insulin or vehicle, submaximally contracted, administered insulin again and relaxation responses recorded. Laminar arteries were also incubated with the mitogen-activated protein kinase (MAPK) inhibitor, PD-98059. Relaxation in response to acetylcholine was not different between arteries and veins, but veins relaxed less in response to insulin than arteries. In arteries incubated with insulin, the subsequent relaxation response to insulin was blunted. Veins had minimal relaxation to insulin regardless of incubation. Arteries incubated with PD-98059 relaxed more in response to insulin than arteries not exposed to PD-98059, indicating that MAPK plays a role in maintenance of basal tone in laminar arteries. A differing response of laminar veins and arteries to insulin-induced relaxation may be important in understanding the link between hyperinsulinemia and laminitis. In vitro induction of vascular dysfunction in response to insulin in laminar arteries may be useful for testing therapeutic interventions and for understanding the pathophysiology of laminitis.

Ultrafiltration of equine digital lamellar tissue

There are no experimentally validated pharmacological means of preventing laminitis; however, locally acting pharmaceutical agents with the potential to prevent laminitis have been identified. Demonstrating therapeutic drug concentrations in lamellar tissue is essential for evaluating the efficacy of these agents. The aim of this study was to develop an experimental technique for repeatedly sampling lamellar interstitial fluid. A technique for placing ultrafiltration probes was developed in vitro using 15 cadaver limbs. Subsequently, lamellar ultrafiltration probes were placed in one forelimb in six living horses. Interstitial fluid was collected continuously from the probes as ultrafiltrate for 4 (n = 4) or 14 days (n = 2). The rate of ultrafiltrate collection was calculated every 12 h. Biochemical analyses were performed on ultrafiltrate collected on night 1 (12-24 h post-implantation) and night 4 (84-96 h post-implantation). Sections surrounding the probe and control tissue from the contralateral limb were harvested, stained with H&E and Masson's trichrome and scored based on the tissue response to the probe. Ultrafiltration probes were placed in the lamellar tissue in all six horses. Ultrafiltrate was collected from these probes at 55 (30-63) μL/h (median [interquartile range]). Fluid production decreased significantly with time from night 3 onwards (P < 0.05). There was no significant change in the constituents of the ultrafiltrate between nights 1 and 4 (P > 0.05). The technique was well tolerated. This study demonstrates that ultrafiltration can be used to sample equine digital lamellar interstitial fluid, and has potential for measuring lamellar drug levels.

Effect of dietary nonstructural carbohydrate content on activation of 5'-adenosine monophosphate-activated protein kinase in liver, skeletal muscle, and digital laminae of lean and obese ponies

Background

In EMS‐associated laminitis, laminar failure may occur in response to energy failure related to insulin resistance (IR) or to the effect of hyperinsulinemia on laminar tissue. 5′‐Adenosine‐monophosphate‐activated protein kinase (AMPK) is a marker of tissue energy deprivation, which may occur in IR.

Hypothesis/Objectives

To characterize tissue AMPK regulation in ponies subjected to a dietary carbohydrate (CHO) challenge.

Animals

Twenty‐two mixed‐breed ponies.

Methods

Immunohistochemistry and immunoblotting for total AMPK and phospho(P)‐AMPK and RT‐qPCR for AMPK‐responsive genes were performed on laminar, liver, and skeletal muscle samples collected after a 7‐day feeding protocol in which ponies stratified on body condition score (BCS; obese or lean) were fed either a low‐CHO diet (ESC + starch, approximately 7% DM; n = 5 obese, 5 lean) or a high‐CHO diet (ESC + starch, approximately 42% DM; n = 6 obese, 6 lean).

Results

5′‐Adenosine‐monophosphate‐activated protein kinase was immunolocalized to laminar keratinocytes, dermal constituents, and hepatocytes. A high‐CHO diet resulted in significantly decreased laminar [P‐AMPK] in lean ponies (P = .03), but no changes in skeletal muscle (lean, P = .33; obese, P = .43) or liver (lean, P = .84; obese, P = .13) [P‐AMPK]. An inverse correlation existed between [blood glucose] and laminar [P‐AMPK] in obese ponies on a high‐CHO diet.

Conclusions and Clinical Importance

Laminar tissue exhibited a normal response to a high‐CHO diet (decreased [P‐AMPK]), whereas this response was not observed in liver and skeletal muscle in both lean (skeletal muscle, P = .33; liver, P = .84) and obese (skeletal muscle, P = .43; liver, P = .13) ponies.

Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score

Breed-related differences may occur in the innate insulin sensitivity (SI) of horses and ponies, an important factor believed to be associated with the risk of laminitis. The aim of this study was to measure the glucose and insulin responses of different breeds of horses and ponies in moderate body condition to a glucose-containing meal and to compare these responses with the indices of SI as determined by a frequently sampled intravenous glucose tolerance test (FSIGT). Eight Standardbred horses, 8 mixed-breed ponies, and 7 Andalusian-cross horses with a mean ± SEM BCS 5.0 ± 0.3 of 9 were used in this study. Each animal underwent an oral glucose tolerance test (OGTT) in which they were fed a fiber-based ration (2.0 g/kg BW) containing 1.5 g/kg BW added glucose, as well as a standard FSIGT with minimal model analysis. The glucose response variables from the OGTT were similar between groups; however, the peak insulin concentration was higher in ponies (94.1 ± 29.1 μIU/mL; P = 0.003) and Andalusians (85.3 ± 18.6; P = 0.004) than in Standardbreds (21.2 ± 3.5). The insulin area under the curve was also higher in ponies (13.5 ± 3.6 IU · min · L(-1); P = 0.009) and Andalusians (15.0 ± 2.7; P = 0.004) than in Standardbreds (3.1 ± 0.6). Insulin sensitivity, as determined by the FSIGT, was lower in Andalusians (0.99 ± 0.18 × 10(-4)/[mIU · min]) than in Standardbreds (5.43 ± 0.94; P < 0.001) and in ponies (2.12 ± 0.44; P = 0.003) than in Standardbreds. Peak insulin concentrations from the OGTT were negatively correlated with SI (P < 0.001; rs = -0.75). These results indicate that there are clear breed-related differences in the insulin responses of horses and ponies to oral and intravenous glucose. All animals were in moderate body condition, indicating that breed-related differences in insulin dynamics occurred independent of obesity.

Effect of Clostridium botulinum toxin type A injections into the deep digital flexor muscle on the range of motion of the metacarpus and carpus, and the force distribution underneath the hooves, of sound horses at the walk

In the treatment of laminitis, reducing deep digital flexor muscle (DDFM) activity might diminish its pull on the distal phalanx, thereby preventing displacement and providing pain relief. Injection of Clostridium botulinum toxin type A into the DDFM of horses is potentially therapeutic. However, the effects of C. botulinum toxin type A on the gait characteristics of sound horses at the walk are not known. The aim of this study was to test if a reduced DDFM activity would lead to (1) alterations of the sagittal range of motion of the metacarpus (SROM) and range of motion of the carpal joint (CROM); (2) changes in the force distribution underneath the hoof (toe vs. heel region: balance index); and (3) changes in the force distribution between the treated and untreated limb (symmetry index). The DDFMs of the left forelimbs of seven sound Royal Dutch Sport Horses were injected with 200 IU C. botulinum toxin type A using electromyography and ultrasound guidance. Measurements using an inertial sensor system and dynamically calibrated pressure plate were performed before and after injections. The SROM and CROM of the treated limb were significantly increased after C. botulinum toxin type A injections. No significant changes were detected in the balance index or in the symmetry index, indicating that no lameness was induced. C. botulinum toxin type A injections into the DDFM of sound horses do not appear to result in substantial gait alterations at the walk.

Risk factors for equine laminitis: a case-control study conducted in veterinary-registered horses and ponies in Great Britain between 2009 and 2011

Laminitis is a highly debilitating disease of the foot known to have a complex and multifactorial aetiology of metabolic, inflammatory, traumatic or vascular origin. The disease has major welfare implications due to unrelenting pain associated with degenerative changes, which often necessitate euthanasia on welfare grounds. Despite this, there have been few high-quality studies investigating risk factors for equine laminitis, and only a limited number of risk factors have been previously investigated. The aim of this study was to conduct a case-control study of risk factors for active episodes of veterinary-diagnosed laminitis in horses and ponies attended by veterinary practitioners in Great Britain, based on multivariable statistical analyses. Questionnaires were received for 1010 animals, comprising 191 laminitis cases and 819 controls. Factors associated with an increased risk of laminitis were weight gain in the previous 3 months, summer and winter months compared to spring, new access to grass in the previous 4 weeks, box rest in the previous week, owner-reported history of laminitis, lameness or foot-soreness after shoeing/trimming, existing endocrinopathic (pituitary pars intermedia dysfunction and equine metabolic syndrome) disease and increasing time since the last anthelmintic treatment. Factors associated with a decreased risk of laminitis were increasing height (cm), feeding of additional supplements in the previous week and transportation in the previous week. Novel associated factors were identified that may aid in the management and prevention of the disease in the veterinary-registered equine population.

Expression of purinergic P2X receptor subtypes 1, 2, 3 and 7 in equine laminitis

Tissue sensitisation and chronic pain have been described in chronic-active laminitis in the horse, making treatment of such cases difficult. Purinergic P2X receptors are linked to chronic pain and inflammation. The aim of this study was to examine the expression of purinergic P2X receptor subtypes 1, 2, 3 and 7 in the hoof, palmar digital vessels and nerve, dorsal root ganglia and spinal cord in horses with chronic-active laminitis (n=5) compared to non-laminitic horses (n=5). Immunohistochemical analysis was performed on tissue sections using antibodies against P2X receptor subtypes 1-3 and 7. In horses with laminitis, there was a reduction in the thickness of the tunica media layer of the palmar digital vein as a proportion of the whole vessel diameter (0.48±0.05) compared to the non-laminitic group (0.57±0.04; P=0.02). P2X receptor subtype 3 was expressed in the smooth muscle layer (tunica media) of the palmar digital artery of horses with laminitis, but was absent in horses without laminitis. There was strong expression of P2X receptor subtype 7 in the proliferating, partially keratinised, epidermal cells of the secondary epidermal lamellae in the hooves of horses with laminitis, but no immunopositivity in horses without laminitis.

Fructokinase, Fructans, Intestinal Permeability, and Metabolic Syndrome: An Equine Connection?

Fructose is a simple sugar present in honey and fruit, but can also exist as a polymer (fructans) in pasture grasses. Mammals are unable to metabolize fructans, but certain gram positive bacteria contain fructanases and can convert fructans to fructose in the gut. Recent studies suggest that fructose generated from bacteria, or directly obtained from the diet, can induce both increased intestinal permeability and features of metabolic syndrome, especially the development of insulin resistance. The development of insulin resistance is driven in part by the metabolism of fructose by fructokinase C in the liver, which results in oxidative stress in the hepatocyte. Similarly, the metabolism of fructose in the small bowel by intestinal fructokinase may lead to increased intestinal permeability and endotoxemia. While speculative, these observations raise the possibility that the mechanism by which fructans induce laminitis could involve intestinal and hepatic fructokinase. Further studies are indicated to determine the role of fructanases, fructose and fructokinase in equine metabolic syndrome and laminitis.