Effects of a supplement containing chromium and magnesium on morphometric measurements, resting glucose, insulin concentrations and insulin sensitivity in laminitic obese horses

Reasons for performing study: Obesity and insulin resistance are risk factors for laminitis in equids and supplements containing chromium and magnesium might improve insulin sensitivity. Hypothesis: A supplement containing chromium, magnesium and other nutraceuticals would alter morphometric measurements, blood variables, and insulin sensitivity in laminitic obese horses. Methods: Twelve previously laminitic obese (body condition score ≥ 7/9) horses were randomly allocated to treatment (n = 6) and control (n = 6) groups and 2 obese horses with clinical laminitis were included in the treatment group. Treated animals received 56 g supplement with 0.25 kg oats once daily for 16 weeks. The supplement contained chromium (5 mg/day as yeast), magnesium (8.8 g/day as oxide/proteinate), and other nutraceuticals. Insulin‐modified frequently sampled i.v. glucose tolerance tests were performed with hay provided at 0, 8 and 16 weeks, and insulin sensitivity was estimated by minimal model analysis. Physical measurements were collected at the same points. Horses were not exercised. Results: Hyperinsulinaemia (>30 µu/ml) was detected in 12 of 14 horses prior to treatment. Glucose and insulin data from one mare with clinical laminitis were excluded because of persistent pain. Mean ± s.d. insulin sensitivity was 0.64 ± 0.62 × 10^?4 l/min/mu prior to treatment for the remaining 13 horses. Time and treatment × time effects were not significant for any of the variables examined, with the exception of resting insulin concentrations, which significantly increased over time (P = 0.018). Health status remained the same. Conclusions: The supplement containing chromium and magnesium evaluated in this study did not alter morphometric measurements, blood variables, resting insulin concentrations or insulin sensitivity in laminitic obese horses. Potential relevance: Additional research is required to determine the appropriate use of chromium and magnesium supplements in horses.     

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.     

Association of Season and Pasture Grazing with Blood Hormone and Metabolite Concentrations in Horses with Presumed Pituitary Pars Intermedia Dysfunction

Background: Pituitary pars intermedia dysfunction (PPID) is a risk factor for pasture‐associated laminitis, which follows a seasonal pattern. Hypothesis: Hormonal responses to season differ between PPID and unaffected horses. Animals: Seventeen horses aged 8–30 years (14 horses ≥ 20 years of age). Methods: Longitudinal observational study. Blood was collected monthly from August 2007 until July 2008 after pasture grazing and again after overnight stall confinement. Blood hormone and metabolite concentrations were measured and pasture grass samples were analyzed to determine carbohydrate content. Analysis of variance analysis for repeated measures was performed. Results: Mean ACTH concentrations varied significantly over time (P < .001), with higher concentrations detected in August, September, and October compared with November–April. Pasture × time effects were detected for glucose and insulin concentrations, with peaks observed in September. Horses were retrospectively allocated to PPID (n = 8) and control (n = 9) groups on the basis of plasma ACTH concentrations. Changes in insulin concentrations over time differed in the PPID group when compared with the control group. Insulin concentrations were positively correlated with grass carbohydrate composition. Conclusions and Clinical Importance: PPID did not affect the timing or duration of the seasonal increase in ACTH concentrations, but higher values were detected in affected horses. Insulin concentrations differed between groups, but hyperinsulinemia was rarely detected. Glucose and insulin concentrations peaked in September when horses were grazing on pasture, which could be relevant to the seasonal pattern of laminitis.     

Continuous intravenous infusion of glucose induces endogenous hyperinsulinaemia and lamellar histopathology in Standardbred horses

Endocrinopathic laminitis is frequently associated with hyperinsulinaemia but the role of glucose in the pathogenesis of the disease has not been fully investigated. This study aimed to determine the endogenous insulin response to a quantity of glucose equivalent to that administered during a laminitis-inducing, euglycaemic, hyperinsulinaemic clamp, over 48 h in insulin-sensitive Standardbred racehorses. In addition, the study investigated whether glucose infusion, in the absence of exogenous insulin administration, would result in the development of clinical and histopathological evidence of laminitis. Glucose (50% dextrose) was infused intravenously at a rate of 0.68 mL/kg/h for 48 h in treated horses (n=4) and control horses (n=3) received a balanced electrolyte solution (0.68 mL/kg/h). Lamellar histology was examined at the conclusion of the experiment. Horses in the treatment group were insulin sensitive (M value 0.039±0.0012 mmol/kg/min and M-to-I ratio (100×) 0.014±0.002) as determined by an approximated hyperglycaemic clamp. Treated horses developed glycosuria, hyperglycaemia (10.7±0.78 mmol/L) and hyperinsulinaemia (208±26.1 μIU/mL), whereas control horses did not. None of the horses became lame as a consequence of the experiment but all of the treated horses developed histopathological evidence of laminitis in at least one foot. Combined with earlier studies, the results showed that laminitis may be induced by either insulin alone or a combination of insulin and glucose, but that it is unlikely to be due to a glucose overload mechanism. Based on the histopathological data, the potential threshold for insulin toxicity (i.e., laminitis) in horses may be at or below a serum concentration of ～200 μIU/mL.     

Optimisation of the frequently sampled intravenous glucose tolerance test to reduce urinary glucose spilling in horses

Reasons for performing study: The frequently sampled i.v. glucose tolerance test (FSIGTT) is used to evaluate glucose and insulin dynamics in horses, but it has not been determined whether urinary glucose spilling (UGS) affects results. Hypothesis: UGS occurs in horses during the FSIGTT and this problem can be minimised by adjusting the dextrose and insulin dosages used. Methods: Six mature mares were included in this study. In the first phase, 6 FSIGTT procedures were performed in each horse to evaluate 6 different dextrose dosages. Six different insulin dosages were evaluated during the second phase of the study after administration of 300 mg/kg bwt dextrose. Area under the glucose (AUCg) and insulin (AUCi) curves were calculated and minimal model analyses performed. UGS was measured in the third and fourth phases of the study during the combined glucose insulin test and established FSIGTT. A new FSIGTT was developed and evaluated. Results: Positive linear effects of dextrose dosage on AUCg, AUCi and acute insulin response to glucose were detected, with AUCg reaching a plateau at doses 200 mg/kg bwt. Insulin dosage had an inverse linear effect on AUCg, but other values remained unaffected. UGS occurred during all 3 tests and was the highest for the established FSIGTT and the lowest for the new FSIGTT. The type of FSIGTT performed did not affect minimal model results. Conclusions: Results indicate that the dextrose dosage of 300 mg/kg bwt used in the established FSIGTT is too high. UGS can be reduced by lowering the dextrose dosage to 100 mg/kg bwt. Potential relevance: A new FSIGTT involving the administration of 100 mg/kg bwt dextrose followed by 20 mu/kg bwt insulin 20 min later is recommended for use in horses because this test provides adequate data for minimal model analysis while minimising UGS.     

Glucose transport in the equine hoof

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

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.     

Insulin dysregulation

Abnormalities of insulin metabolism include hyperinsulinaemia and insulin resistance, and these problems are collectively referred to as insulin dysregulation in this review. Insulin dysregulation is a key component of equine metabolic syndrome: a collection of endocrine and metabolic abnormalities associated with the development of laminitis in horses, ponies and donkeys. Insulin dysregulation can also accompany prematurity and systemic illness in foals. Causes of insulin resistance are discussed, including pathological conditions of obesity, systemic inflammation and pituitary pars intermedia dysfunction, as well as the physiological responses to stress and pregnancy. Most of the discussion of insulin dysregulation to date has focused on insulin resistance, but there is increasing interest in hyperinsulinaemia itself and insulin responses to feeding. An oral sugar test or in‐feed oral glucose tolerance test can be performed to assess insulin responses to dietary carbohydrates, and these tests are now recommended for use in clinical practice. Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research. Insulin resistance exacerbates hyperinsulinaemia, and insulin sensitivity can be measured by performing a combined glucose‐insulin test or i.v. insulin tolerance test. In both of these tests, exogenous insulin is administered and the rate of glucose uptake into tissues measured. Diagnosis and management of hyperinsulinaemia is recommended to reduce the risk of laminitis. The term insulin dysregulation is introduced here to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome.     

Equine laminitis: Ultrastructural lesions detected in ponies following hyperinsulinaemia

Reasons for performing study: Anatomical changes in the hoof lamellar tissue induced by prolonged hyperinsulinaemia have not been described previously. Analysis of the induced lesions may promote understanding of hyperinsulinaemic laminitis pathogenesis and produce clinical benefit. Objectives: To use light and transmission electron microscopy (TEM) to document hoof lamellar lesions in ponies clinically lame after prolonged hyperinsulinaemia. Methods: Nine clinically normal, mature ponies were allocated randomly to either a treatment group (n = 5) or control group (n = 4). The treatment group received insulin via a modified, prolonged euglycaemic hyperinsulinaemic clamp technique (EHCT) and were subjected to euthanasia when clinical signs of Obel grade II laminitis occurred. The control group was sham treated with an equivalent volume of 0.9% saline and killed at 72 h. Lamellar tissues of the right front feet were harvested and processed for TEM. Results: Lamellae from insulin treated ponies were attenuated and elongated with many epidermal basal cells (EBC) in mitosis. Unlike carbohydrate induced laminitis in horses there was no global separation at the lamellar dermal/epidermal interface among ponies. Sporadic EBC basement membrane (BM) separation was associated with the proximity of infiltrating leucocytes. In 2 ponies, the lamellar BM was thickened. The number of hemidesmosomes/μm of BM was decreased in all insulin treated ponies. Conclusions: Prolonged hyperinsulinaemia causes unique lamellar lesions normally characteristic of acute and chronic laminitis. Lamellar proliferation may be an insulin effect through its mitogenic pathway. Aberrant lamellar mitosis may lengthen and weaken the lamellar, distal phalanx attachment apparatus and contribute to the clinical signs that developed. Potential relevance: The study shows that insulin alone, in higher than normal circulating concentrations, induces profound, changes in lamellar anatomy. Medical control of insulin resistance and hyperinsulinaemia may ameliorate lesions and produce clinical benefit.     

Measurement of C‐peptide concentrations and responses to somatostatin,glucose infusion,and insulin resistance in horses

Reasons for performing study: Hyperinsulinaemia is detected in horses with insulin resistance (IR) and has previously been attributed to increased pancreatic insulin secretion. Connecting peptide (C‐peptide) can be measured to assess pancreatic function because it is secreted in equimolar amounts with insulin and does not undergo hepatic clearance. Hypothesis: A human double antibody radioimmunoassay (RIA) detects C‐peptide in equine serum and concentrations would reflect responses to different stimuli and conditions. Methods: A validation procedure was performed to assess the RIA. Six mature mares were selected and somatostatin administered i.v. as a primed continuous rate infusion, followed by 50 nmol human C‐peptide i.v. Insulin and C‐peptide concentrations were measured in horses (n = 6) undergoing an insulin‐modified frequently sampled i.v. glucose tolerance test, and in horses with insulin resistance (n = 10) or normal insulin sensitivity (n = 20). Results: A human RIA was validated for use with equine sera. Endogenous C‐peptide secretion was suppressed by somatostatin and median (range) clearance rate was 0.83 (0.15–1.61) ml/min/kg bwt. Mean ± s.d. C‐peptide‐to‐insulin ratio significantly (P = 0.004) decreased during the glucose tolerance test from 3.60 ± 1.95 prior to infusion to 1.03 ± 0.18 during the first 20 min following dextrose administration. Median C‐peptide and insulin concentrations were 1.5‐ and 9.5‐fold higher, respectively in horses with IR, compared with healthy horses. Conclusions: Endogenous C‐peptide secretion decreases in response to somatostatin and increases after dextrose infusion. Results suggest that relative insulin clearance decreases as pancreatic secretion increases in response to dextrose infusion. Hyperinsulinaemia in insulin resistant horses may be associated with both increased insulin secretion and decreased insulin clearance. Potential relevance: Both C‐peptide and insulin concentrations should be measured to assess pancreatic secretion and insulin clearance in horses.     

Multicentre,controlled, randomised and blinded field study comparing efficacy of suxibuzone and phenylbutazone in lame horses

Reasons for performing study: In horses, it has been demonstrated that suxibuzone (SBZ) has a lower gastric ulcerogenic effect than phenylbutazone (PBZ). However, no field trials have been reported comparing the efficacy of the drugs in alleviating lameness. Objectives: To compare the therapeutic effect of SBZ to that of PBZ when administered orally in lame horses. Acceptability of both products was also compared. Methods: Lame horses (n = 155) were used in a multicentre, controlled, randomised and double‐blinded clinical trial. Horses were treated orally with either SBZ or PBZ at equivalent therapeutic dosages. PBZ was given to 79 horses at a dose of 4.4 mg/kg bwt/12 h for 2 days, followed by 2.2 mg/kg bwt/12 h for 6 days. SBZ was given to 76 horses at 6.6 mg/kg bwt/12 h for 2 days, followed by 3.3 mg/kg bwt/12 h for 6 days. Efficacy of treatments was evaluated by clinicians in equine practices according to lameness progression throughout the study. Product ingestion was checked daily to evaluate product acceptability. Results: Although SBZ showed a statistically significant tendency to have a better efficacy than PBZ (Odds ratio = 2.7; P = 0.016), significance dissipated once the analysis was adjusted for some imbalanced baseline covariates, confirming that they were actually related to the apparent advantage of SBZ over PBZ. Product acceptability was significantly higher in the SBZ group than in the PBZ group (96.1% vs. 77.2%; P = 0.001). Conclusions: SBZ and PBZ did not show significant differences in alleviating lameness in horses. However, SBZ had better product acceptability when administered orally with some food. Potential relevance: SBZ is a good therapeutic alternative to PBZ in horses since there is no significant difference in alleviating lameness between the 2 therapies.     

Effects of dexamethasone on glucose dynamics and insulin sensitivity in healthy horses

OBJECTIVE: To determine effects of dexamethasone on glucose dynamics and insulin sensitivity in healthy horses. ANIMALS: 6 adult Standardbreds. PROCEDURES: In a balanced crossover study, horses received dexamethasone (0.08 mg/ kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution (control treatment) during a 21-day period. Horses underwent a 3-hour frequently sampled IV glucose tolerance test (FSIGT) 2 days after treatment. Minimal model analysis of glucose and insulin data from FSIGTs were used to estimate insulin sensitivity (Si), glucose effectiveness (Sg), acute insulin response to glucose (AIRg), and disposition index. Proxies for Si (reciprocal of the inverse square of basal insulin concentration [RISQI]) and beta-cell responsiveness (modified insulin-to-glucose ratio [MIRG]) were calculated from basal plasma glucose and serum insulin concentrations. RESULTS: Mean serum insulin concentration was significantly higher in dexamethasone-treated horses than control horses on days 7, 14, and 21. Similarly, mean plasma glucose concentration was higher in dexamethasone-treated horses on days 7, 14, and 21; this value differed significantly on day 14 but not on days 7 or 21. Minimal model analysis of FSIGT data revealed a significant decrease in Si and a significant increase in AIRg after dexamethasone treatment, with no change in Sg or disposition index. Mean RISQI was significantly lower, whereas MIRG was higher, in dexamethasone-treated horses than control horses on days 7, 14, and 21. CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed marked insulin resistance in healthy horses after 21 days of dexamethasone administration. Because insulin resistance has been associated with a predisposition to laminitis, a glucocorticoid-induced decrease in insulin sensitivity may increase risk for development of laminitis in some horses and ponies.     

Use of proxy measurements of insulin sensitivity and insulin secretory response to distinguish between normal and previously laminitic ponies

Reasons for performing study: Insulin resistance may be a risk factor for pasture‐associated laminitis. Diagnosis of insulin resistance could help identify individuals at increased risk of laminitis. Objective: To calculate proxy measurements of insulin sensitivity (reciprocal of the square root of insulin: RISQI and quantitative insulin sensitivity check index: QUICKI) and insulin secretory response (modified insulin‐to‐glucose ratio: MIRG) based on basal glucose and insulin concentrations in normal (NP) and previously laminitic (PLP) ponies. Methods: Proxies were calculated in 7 NP and 5 PLP from 20 separate measurements of insulin and glucose taken in spring, summer and winter when ponies were adapted to eating either pasture or hay. Proxies were RISQI: Insulin^‐0.5, QUICKI: 1/(log[fasting Insulin]+ log[fasting Glucose]) and MIRG: (800?0.3×[Insulin‐50]²)/[Glucose‐30]. A modified insulin‐to‐glucose ratio for ponies (MIGRP) was investigated using: (3000?0.012 ×[Insulin‐500]²)/[Glucose‐30]. Statistical analysis used linear mixed models. Results: Diet did not significantly affect measurements, so values were pooled for further analysis. RISQI (mean ± s.d.) was lower in PLP (0.26 ± 0.15 [mu/l]^‐0.5) than NP (0.29 ± 0.12 [mu/l]^‐0.5; P = 0.05). QUICKI was lower in PLP (0.31 ± 0.05) than NP (0.33 ± 0.04; P = 0.047). There was no difference in MIRG between NP and PLP. MIGRP (median [interquartile range]) was greater in PLP (4.0 [7.9][mu_ins]²/10·l·mg_gluc) than NP (2.6 [3.2][mu_ins]²/10·l·mg_gluc; P = 0.022). In spring, NP had higher RISQI and QUICKI and lower MIGRP than PLP (P<0.001). In PLP, RISQI and QUICKI were higher in summer than spring (P<0.02) and MIGRP was lower in summer than other seasons (P<0.01). In NP, RISQI, QUICKI and MIGRP were each different between seasons (P<0.017). MIRG did not vary with season. Conclusions: RISQI, QUICKI and MIGRP, but not MIRG, differentiated between NP and PLP. None of the proxies accurately identified individual PLP. Seasonal changes in insulin sensitivity and insulin secretory response were apparent. Potential relevance: Current proxy measurements cannot determine an individual's laminitis susceptibility. MIGRP may be useful in hyperinsulinaemic animals.     

The timeline of lamellar basement membrane changes during equine laminitis development

Reasons for performing study: The timing of lamellar basement membrane (BM) changes occurring during laminitis development is incompletely understood. Objectives: To determine the temporal progression of lamellar BM changes and whether laminin‐332 (Ln‐332) γ2 cleavage products are generated during laminitis development. Methods: Eight clinically normal Standardbred horses were allocated into treatment (n = 5) or sham (n = 3) groups. The treatment group received, via nasogastric intubation, an oligofructose (OF) bolus (10 g/kg bwt) while the sham group was given water. Laminitis induction proceeded for 48 h followed by euthanasia. Lamellar biopsies were obtained prior to dosing and at intervals during the treatment period for analysis (at 12, 18, 24, 30 and 36 h and at 48 h following euthanasia). Results: Changes in lamellar collagen type IV and Ln‐332 were first observed at 12 h post dosing. A unique pattern of reactivity for the Ln‐332 γ2 antibody D4B5 occurred, in which reactivity was observed only in lamellar tissue affected by laminitis. No bioactive Ln‐332 γ2 proteolytic fragments were detected in lamellar samples. Conclusions: Basement membrane changes occurred early during the laminitis process. Direct Ln‐332 γ2 cleavage to release biologically active products did not appear to occur. Thus loss of stability or protein interaction of the BM is probably responsible for the γ2 specific reactivity observed. Potential relevance: Basement membrane changes may a first step in lamellar failure occurring prior to detection with conventional methods. Thus, more sensitive detection methods of BM changes are required to study laminitis development.     

Ethyl pyruvate diminishes the inflammatory response to lipopolysaccharide infusion in horses

Reasons for performing the study: Endotoxaemia contributes to morbidity and mortality in horses with colic due to inflammatory cascade activation. Effective therapeutic interventions are limited for these horses. Ethyl pyruvate (EP), an anti‐inflammatory agent that alters the expression of proinflammatory cytokines, improved survival and organ function in sepsis and gastrointestinal injury in rodents and swine. Therapeutic efficacy of EP is unknown in endotoxaemic horses. Objectives: Determine the effects of EP on signs of endotoxaemia and expression of proinflammatory cytokines following administration of lipopolysaccharide (LPS) in horses. Methods: Horses received 30 ng/kg bwt LPS in saline to induce signs of endotoxaemia. Next, horses received lactated Ringer's solution (LRS), (n = 6), 150 mg/kg bwt EP in LRS, (n = 6), or 1.1 mg/kg bwt flunixin meglumine (FM), (n = 6). Controls received saline followed by LRS (n = 6). Physical examinations, behaviour pain scores and blood for clinical pathological testing and gene expression were obtained at predetermined intervals for 24 h. Results: Lipopolysaccharide infusion produced clinical and clinicopathological signs of endotoxaemia and increased expression of tumour necrosis factor alpha (TNFα), interleukin 6 (IL‐6) and IL‐8 (P<0.001) compared with controls. Leucopenia and neutropenia occurred in all horses that received LPS. Horses treated with EP and FM had significantly (P<0.0001) reduced pain scores compared with horses receiving LPS followed by LRS. Flunixin meglumine was significantly more effective at ameliorating fever compared with EP. Both EP and FM significantly diminished TNFα expression. Ethyl pyruvate significantly decreased, but FM significantly increased, IL‐6 expression. Neither EP nor FM altered IL‐8 expression. Conclusions and potential relevance: Ethyl pyruvate administered following LPS diminished the clinical effects of endotoxaemia and decreased proinflammatory gene expression in horses. Ethyl pyruvate suppressed expression of proinflammatory cytokines better than FM. However, FM was a superior anti‐pyretic compared with EP. Ethyl pyruvate may have therapeutic applications in endotoxaemic horses.     

Laminar leukocyte accumulation in horses with carbohydrate overload-induced laminitis

Background: While there is evidence of laminar leukocyte infiltration in black walnut extract (BWE)‐induced laminitis, there is no such evidence for carbohydrate overload (CHO) laminitis. Objective: To assess presence of leukocytes and signs of epidermal stress/injury in the laminar tissue from horses with CHO‐induced laminitis. Animals: Twenty‐four adult horses. Methods: Immunohistochemistry for myeloid cell markers calprotectin (CP) and monocyte‐specific marker (CD163) was performed on laminar sections obtained from 2 groups of horses in the CHO model: the developmental time point (DTP) group (n = 6) and the onset of lameness (LAM) group (n = 6), and a control (CON) group (n = 8). Results: DTP was characterized by an increase in CP⁺ leukocytes (7.8‐fold increase versus CON, P < .001), and LAM time point was characterized by a more marked increase in laminar CP⁺ (108.5‐fold, P < .001) and mild increase in CD163⁺ (1.9‐fold, P= .007) cell counts. Increased CP epidermal signal (indicating epidermal stress or injury) occurred consistently at the LAM time point, although histological evidence of basement membrane (BM) detachment was minor, only being present in 3/6 horses. Conclusions and Clinical Relevance: Maximal laminar leukocyte infiltration and epithelial stress occurred at the onset of lameness in the CHO model showing a different temporal pattern from the BWE model, where maximal leukocyte infiltration clearly precedes epithelial stress. Leukocyte infiltration before major histological changes in the CHO model indicates that leukocyte infiltration can be a cause of and not a reaction to BM degradation and structural failure.     

Glucose tolerance and insulin sensitivity in ponies and Standardbred horses

The existence of an innate insulin insensitivity in ponies was investigated and compared with the situation in larger breeds of horse. Ponies that were fat or had previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bodyweight [bwt]) than normal ponies or Standardbreds. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic groups. The relevance of these findings in regulation of carbohydrate and lipid metabolism, and their role in the pathogenesis of hyperlipaemia, are discussed.     

Age and body weight effects on glucose and insulin tolerance in colony cats maintained since weaning on high dietary carbohydrate

High dietary carbohydrate is suggested to promote development of diabetes mellitus in cats. Glucose tolerance, insulin sensitivity, and insulin secretion were assessed in young [0.8–2.3 (median = 1.1) years, n = 13] and mature [4.0–7.0 (median 5.8) years, n = 12] sexually intact females of a large (n ? 700) feline colony in which only dry‐type diets (35% metabolizable energy as carbohydrate) were fed from weaning. Insulin sensitivity was assessed from the ‘late‐phase’ (60–120 min) plasma insulin response of intravenous glucose tolerance tests (IVGTTs) and from fractional change in glycaemia from baseline 15 min after an insulin bolus (0.1 U/kg, i.v.). Insulin secretion was assessed from the ‘early‐phase’ (0–15 min) plasma insulin response of IVGTTs. Compared to the young cats, the mature cats had greater body weights [2.3–3.8 (median = 2.9) vs. 3.0–6.3 (median = 4.0) kg, p < 0.01], greater late‐phase insulin responses (p < 0.05), lower insulin‐induced glycaemic changes (p = 0.06), lower early‐phase insulin responses (p < 0.05), and non‐significantly different rates of glucose disposal. The late‐phase insulin response was correlated with body weight and age (p < 0.05). When group assignments were balanced for body weight, the age‐group differences and correlations became non‐significant. The findings indicate that body weight gain is more likely than dry‐type diets to induce the pre‐diabetic conditions of insulin resistance and secretion dysfunction.     

A 90‐day adaptation to a high glycaemic diet alters postprandial lipid metabolism in non‐obese horses without affecting peripheral insulin sensitivity

High glycaemic feeds are associated with the development of insulin resistance in horses. However, studies that evaluated the effect of high glycaemic feeds used horses that either ranged in body condition from lean to obese or were fed to increase body condition over a period of months; thus, the ability of high glycaemic feeds to induce insulin resistance in lean horses has not been determined. This study evaluated the insulin sensitivity of 18 lean horses fed a 10% (LO; n = 6), 20% (MED; n = 6) or 60% (HI; n = 6) non‐structural carbohydrate complementary feed for 90 days. Although both the MED and HI diets increased insulinaemic responses to concentrate feeding in relation to the LO diet (p > 0.05), neither induced insulin resistance, as assessed by glucose tolerance test, following the 90‐day feeding trial. Interestingly, the post‐feeding suppression of plasma non‐esterified fatty acids was less pronounced in HI‐fed horses (p = 0.054) on days 30 and 90 of the study, potentially indicating that insulin‐induced suppression of adipose tissue lipolysis was reduced. As insulin‐resistant animals often have elevated plasma lipid concentrations, it is possible that altered lipid metabolism is an early event in the development of insulin resistance. The effects of high glycaemic feeds that are fed for a longer duration of time, on glucose and lipid metabolism, should be investigated further.