Article

The oral glucose test predicts laminitis risk in ponies fed a diet high in nonstructural carbohydrates

November 2017
Domestic Animal Endocrinology 63

DOI:10.1016/j.domaniend.2017.10.008

Authors:

Melody A de Laat

Queensland University of Technology

Chris Pollitt

The University of Queensland

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The aim of this study was to investigate the relationship between laminitis development in ponies and insulin/glucose concentrations in response to the oral glucose test (OGT) and a dietary challenge high in nonstructural carbohydrates (NSCs). After undergoing an OGT (1 g dextrose/kg BW in feed), 37 ponies with 2-h serum insulin concentrations ranging from 22 to 1,133 μIU/mL were subjected to a diet challenge period (DCP), consuming 12 g NSC/kg BW/d for up to 18 d. Insulin and glucose responses were measured on day 2 of the DCP. Clinical laminitis was diagnosed by blinded experts and confirmed radiographically. Basal ACTH levels and clinical signs were assessed to investigate concurrent putative pituitary pars intermedia dysfunction (PPID). The diet induced Obel grade 1 or 2 laminitis in 14 ponies (38%). The ponies that developed laminitis had higher maximum concentrations of blood glucose (P = 0.04) and serum insulin (P = 0.02) in response to the diet. The geometric mean (95% CI) blood glucose concentration for laminitis cases was 14.9 (12.9-17.2) mM, compared to 10.7 (9.2-12.5) mM for ponies who did not develop laminitis. Similarly, the geometric mean (95% CI) for serum insulin was 396 (301-520) μIU/mL for laminitis cases, compared to 216 (148-316) μIU/mL for ponies who did not develop laminitis. Laminitis incidence was likewise associated with insulin concentrations measured during the OGT. Laminitis occurred at frequencies of 0% (0/7) if postdextrose insulin (μIU/mL) was <50; 35% (8/23) if insulin was 50 to 195; and 86% (6/7) if insulin was >195 μIU/mL. Basal ACTH concentrations were above seasonally accepted reference ranges in 16/37 ponies, and 8 of these animals (50%) developed laminitis. This included all 5 ponies in the study that had clinical signs of PPID (100%). In contrast, hyperinsulinemia and laminitis occurred in only 3/11 ponies (27%) with elevated ACTH concentrations and no clinical signs of PPID (P = 0.009). Thus, laminitis occurrence was associated with higher glucose and insulin responses to both the OGT and challenge diet, and the frequency of laminitis can be predicted based on insulin and glucose hyperresponsiveness to these oral carbohydrate challenges.

Value of measuring markers of lipid metabolism in horses during an oral glucose test

Article

Full-text available

Sep 2024
J VET INTERN MED

Background Characterizing the lipid response to an oral glucose test (OGT) might improve our understanding of Equine Metabolic Syndrome. Hypothesis/Objectives To describe the effects of an OGT on lipid metabolism and determine the value of measuring triglyceride and nonesterified fatty acid (NEFA) concentrations in hyperinsulinemic (HI) and insulin‐resistant (IR) horses. Animals Twenty horses including 7 HI‐IR horses, 4 HI‐non‐IR horses, and 9 non‐HI‐non‐IR horses (control). Methods Cross‐sectional design. Horses underwent an OGT, with blood samples collected at 0, 60, 90, and 120 minutes. Insulin, glucose, triglyceride, and NEFA concentrations were measured and compared over time and between groups, with P < .05 considered significant. Results In all horses, the OGT had a significant effect on triglyceride concentrations (median [interquartile range]: .35 [.30‐.50] mmol/L at 0 minute vs .25 [.21‐.37] mmol/L at 120 minutes, P = .005) and on NEFA concentrations (.1 [.1‐.2] mEq/L at 0 minute vs .05 [.05‐.1] mEq/L at 120 minutes, P = .0009). However, horses with HI and IR had higher triglyceride areas under the curve (AUC, 79.46 ± 46.59 vs 33.32 ± 6.75 mmol/L*min, P = .01) as well as NEFA AUC (9.1 ± 2.9 vs 6.0 ± 6.8 mEq/L*min, P = .03) than control horses. No significant difference was detected between control and HI non‐IR horses. Conclusions and Clinical Importance Determining triglyceride and NEFA concentrations might help assess tissue insulin resistance during an OGT.

Comparison of one novel and four established diagnostic tests for insulin dysregulation in ponies

Article

Dec 2023
VET J

Demographic, morphologic, hormonal and metabolic factors associated with the rate of improvement from equine hyperinsulinaemia-associated laminitis

Article

Full-text available

Jan 2022
BMC Vet Res

Abstract Background Although several studies have investigated factors associated with the onset and occurrence of hyperinsulinaemia-associated laminitis (HAL), few have examined the factors associated with the rate of improvement during recovery from an acute bout of the disease. This observational study sought to discover if a range of demographic, morphologic, hormonal and metabolic variables are associated with the improvement rate from HAL in 37 naturally-occurring cases identified by 16 clinics across Germany. Each case was evaluated for laminitis severity on the day of inclusion in the trial (d 0), then after 4, 9, 14, 25 and 42 d. The horses were managed according to best clinical practice including restricting exercise and prescribing a diet of hay-only, for a minimum of 9 d. Blood samples were also collected during each evaluation, except on d 9, and analysed for glucose, insulin, ACTH and leptin. Results Based on individual clinical laminitis scores plotted against time, most horses improved markedly within 2 weeks, with a ‘fast group’ (n = 27) having a median (interquartile range) score on a 12-point scale of 0 (0–2) by d 14. However, there was a clear disparity within the total cohort, as ~ 1 in 4 horses demonstrated much slower improvement, with a median score of 5 (4–7) by d 14, or a marked relapse thereafter (‘slow group’, n = 10). Horses in the slow improvement group were younger (12.5 (8.8–16.3) vs 17 (14–24) yr; P = 0.008), but were not more likely to be heavier, male, very fat, to have presented with a previous history of laminitis or elevated ACTH concentrations, or to be receiving pergolide treatment. Of the hormonal and metabolic parameters measured, glucose and insulin concentrations were within the normal range following transition to the hay-only diet, but were higher in the group that failed to improve quickly, with a small but significant difference being evident on d 4, 14 and 25 for glucose (11 to 16%; P

Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non‐insulin dysregulated controls

Article

Full-text available

Jul 2021
EQUINE VET J

Background Controlling postprandial hyperinsulinaemia is important in insulin dysregulated (ID) horses to reduce the risk of laminitis. Objectives To evaluate postprandial insulin responses of ID versus non‐insulin dysregulated (NID) horses to feedstuffs varying in nonstructural carbohydrate (NSC) and crude protein (CP). Study design Randomised crossover. Methods Eighteen adult mixed‐breed horses (13.3 ± 2.2 years; 621 ± 78.8 kg) were individually fed [~1 g/kg body weight (BW)] specific feedstuffs within two crossover studies. Eight ID and eight NID were used in Study A, and 11 ID and 5 NID in Study B. In Study A, all horses were randomly fed once: cracked corn (CC: ~74% NSC & ~9% CP), ration balancer with low protein (RB‐LP: ~15% NSC & ~17% CP), ration balancer with high protein (RB‐HP: ~14% NSC and ~37% CP) and 50:50 mixture of RB‐LP:RB‐HP (MIX‐P). In Study B, horses were randomly fed once: CC, RB‐HP, steam‐flaked corn (SF: ~73% NSC & ~10% CP), oat groats (OG: ~64% NSC & ~14% CP) and a low NSC pellet (L‐NSC: ~6% NSC & ~12% CP). Blood was collected for insulin determination [radioimmunoassay (RIA)] before and 30, 60, 75, 90, 105, 120, 150, 180, 210 and 240‐minute post‐feeding in Study A and at 60‐minute in Study B. Data were analysed via analysis of variance (ANOVA) for repeated measures after any required transformations. Results ID horses had significantly greater insulin responses (AUCi) than NID for all diets in both studies (P < .001; ID 22 362 ± 10 298 µIU/mL/min & NID 6145 ± 1922 µIU/mL/min). No effect of diet on AUCi for NID (P = .2), but in ID, the CC (32 000 ± 13 960 µIU/mL/min) AUCi was higher than RB‐LP (P = .01; 18 977 ± 6731 µIU/mL/min). ID insulin (T60) was lower for the L‐NSC (57.8 ± 18.5 µIU/mL) versus all other diets (P < .02; 160.1 ± 91.5 µIU/mL). Main limitations Small numbers of horses; no ponies. Conclusions NSC appears to be the main driver of the postprandial insulin response. ID horses respond disproportionately to feeding even small amounts of low/moderate NSC feedstuffs. Data on possible dietary thresholds for postprandial insulin responses cannot be extrapolated from NID horses.

Metabolic profile distinguishes laminitis- susceptible and -resistant ponies before and after feeding a high sugar diet

Article

Full-text available

Jan 2021
BMC Vet Res

Background: Insulin dysregulation (ID) is a key risk factor for equine endocrinopathic laminitis, but in many cases ID can only be assessed accurately using dynamic tests. The identification of other biomarkers could provide an alternative or adjunct diagnostic method, to allow early intervention before laminitis develops. The present study characterised the metabolome of ponies with varying degrees of ID using basal and postprandial plasma samples obtained during a previous study, which examined the predictive power of blood insulin levels for the development of laminitis, in ponies fed a high-sugar diet. Samples from 10 pre-laminitic (PL-subsequently developed laminitis) and 10 non-laminitic (NL-did not develop laminitis) ponies were used in a targeted metabolomic assay. Differential concentration and pathway analysis were performed using linear models and global tests. Results: Significant changes in the concentration of six glycerophospholipids (adj. P ≤ 0.024) and a global enrichment of the glucose-alanine cycle (adj. P = 0.048) were found to characterise the response of PL ponies to the high-sugar diet. In contrast, the metabolites showed no significant association with the presence or absence of pituitary pars intermedia dysfunction in all ponies. Conclusions: The present results suggest that ID and laminitis risk are associated with alterations in the glycerophospholipid and glucose metabolism, which may help understand and explain some molecular processes causing or resulting from these conditions. The prognostic value of the identified biomarkers for laminitis remains to be investigated in further metabolomic trials in horses and ponies.

Effects of an anti-IGF-1 receptor monoclonal antibody on laminitis induced by prolonged hyperinsulinaemia in Standardbred horses

Article

Full-text available

Sep 2020
PLOS ONE

Currently, there are no registered veterinary drugs for the treatment of endocrinopathic equine laminitis, and although this form of the disease is known to be caused by prolonged hyperinsulinaemia, the mechanism of insulin toxicity is unclear. One possibility is that high concentrations of insulin activate IGF-1 receptors (IGF-1R) in lamellar tissue, leading to uncontrolled cell proliferation and epidermal lamellar dysregulation. An equinized version of a human anti-IGF-1R therapeutic monoclonal antibody (mAb11) was generated to test this theory, using a modification of the prolonged euglycaemic-hyperinsulinaemic clamp technique. Healthy Standardbred horses were infused for 48 h with 0.9% saline (negative-control, n = 6), a combination of insulin (4.5 mIU/kgBW/min) and a variable infusion of 50% glucose to maintain euglycaemia (positive-control, n = 6), or insulin and glucose, preceded by a low dose of mAb11 (20 mg), designed to treat one foot only and delivered by retrograde infusion into one forelimb (mAb-treated, n = 7). Maximum insulin concentrations were 502 ± 54.4 and 435 ± 30.4 μIU/mL in the positive-control and mAb11-treated groups, respectively (P = 0.33). While the control group remained healthy, all the insulin-treated horses developed laminitis within 30 h, as judged by clinical examination, foot radiographs and histological analysis. Some effects of insulin were not attenuated by the antibody, however, relative to the positive-control group, horses treated with mAb11 showed less sinking of the distal phalanx (P < 0.05) and milder histological changes, with markedly less elongation at the tips of the secondary epidermal lamellae (P < 0.05). These differences were apparent in both front feet and were statistically significant when the values for both feet were combined. The results confirm that IGF-1R may have a role in insulin-induced laminitis and suggest that mAb11 warrants further research as a potential agent to prevent or treat the disease.

Effect of Phenylbutazone Administration on Insulin Sensitivity in Horses With Insulin Dysregulation

Article

Full-text available

Feb 2025
J VET INTERN MED

Background Phenylbutazone is prescribed to manage pain caused by hyperinsulinemia‐associated laminitis. Phenylbutazone reduces glucose and insulin concentrations in horses with insulin dysregulation (ID) but the underlying mechanism of action is unknown. Hypothesis/Objectives Investigate the effect of phenylbutazone on tissue insulin sensitivity in horses. It is hypothesized that the reduced glucose and insulin concentrations in horses with ID receiving phenylbutazone are mediated by a higher tissue insulin sensitivity. Animals Fifteen light breed horses, including seven with ID. Methods Randomized cross‐over study. Horses underwent a modified frequently sampled intravenous glucose tolerance test (mFSIGTT) after 8 days of treatment with phenylbutazone (4.4 mg/kg IV daily) or placebo (5 mL 0.9% saline IV daily). After a 10‐day washout period, horses received the alternative treatment for 8 days and a second mFSIGTT. Minimal model analysis was performed, and the effects of ID status and phenylbutazone were investigated with p < 0.05 considered significant. Results In horses with ID, phenylbutazone increased tissue insulin sensitivity index (median [interquartile range]: 0.39 [0.14–0.74] vs. 0.56 [0.55–1.18] ×10⁻⁴ L/mIU/min, p = 0.03), and decreased glucose (21 726 [19 040–24 948] vs. 22 909 [22 496–26 166] mg/dL × min, p = 0.02) and insulin (19 595 [16 147—29 698] vs. 22 752 [20 578—31 826] μIU/mL × min, p = 0.03) areas under the curves. No effect was detected in horses administered placebo. Conclusion and Clinical Importance Phenylbutazone reduces insulin concentration in horses with ID by modulating tissue insulin sensitivity, suggesting that its relevance in the management of ID can extend beyond laminitis‐associated pain.

Nutraceutical Supplement Mitigates Insulin Resistance in Horses with a History of Insulin Dysregulation During a Challenge with a High-Starch Diet

Article

Full-text available

Nov 2024

Simple Summary Insulin dysregulation (ID) is associated with an increased risk of laminitis which often necessitates the need for clinical intervention or euthanasia in severe cases. The prophylactic supplementation of nutraceuticals could mitigate ID in susceptible horses, improve horse wellbeing, and reduce the incidence and (or) severity of this debilitating disease. Accordingly, this study was conducted to test the hypothesis that nutraceutical supplementation containing a mixture of omega-3 fatty acid sources, glutamine, vitamin E, and an active yeast mitigates insulin resistance in horses with a prior history of ID during a four-week challenge with a high-starch diet. A combined glucose–insulin tolerance test was used to assess the insulin sensitivity in each horse. After four weeks of treatment, horses supplemented with the nutraceutical had 61% greater blood glucose clearance rates and a reduced time necessary to return to the baseline concentration following a glucose–insulin bolus compared to placebo-treated horses. Likewise, plasma insulin concentrations returned to baseline concentrations at 75 min post-bolus for nutraceutical-treated horse, whilst those supplemented with the placebo remained in a hyperinsulinemic state. Thus, it was concluded that (1) the dietary high-starch challenge used in this study was sufficient to reduce the insulin sensitivity in ID-prone horses and (2) the prophylactic supplementation of the nutraceutical blend mitigated the negative effects of the dietary starch challenge on insulin sensitivity ID in susceptible horses.

Development of a Web App to Convert Blood Insulin Concentrations among Various Immunoassays Used in Horses

Article

Full-text available

Aug 2023

Simple Summary In horses, the hormone insulin is frequently measured in blood samples, as increased concentrations can lead to a painful condition of the hoof called laminitis. The early detection of an increased insulin concentration is essential for animal welfare. There is considerable disagreement between different measurement methods (assays) for insulin concentration, however, meaning that the threshold for diagnosis must be determined for each assay individually. To alleviate this requirement, we derived formulas from previous assay comparisons, to convert the values from one assay to another, and made them available through a free web app. Over a wide range of commonly used insulin assays, veterinarians can now compare their measurements to previously published values. Scientists can also use the app to compare publications using different assays. Abstract The measurement of the blood insulin concentration, and comparison to cut-offs, is essential in diagnosing insulin dysregulation, a common equine endocrinopathy. However, different insulin assays provide disparate results. We aimed to ease comparison between assays by compiling original and published data into a web app to convert insulin measurements from one assay to another. Data were available for ADVIA Centaur insulin chemiluminescent immunoassay (CLIA), Beckman Coulter insulin radioimmunoassay (RIA), Immulite 1000 CLIA, Immulite 2000 CLIA, Immulite 2000 XPi CLIA, Mercodia equine insulin enzyme-linked immunosorbent assay (ELISA), and Millipore porcine insulin RIA. Linear models were fitted for 13 assay pairs using non-decreasing splines, and integrated into this app. Assay comparisons including data from several studies showed a lower performance. This indicates technical variation between laboratories, which has not been described before, but is relevant when diagnostic measurements and cut-offs are provided by different laboratories. Nevertheless, the models’ overall high performance (median r² = 0.94; range 0.57–1.00) supports their use to interpret results from diagnostic insulin measurements when the reference assay is unavailable, and to compare values obtained from different assays.

Palatability, glycemic, and insulinemic responses to various carbohydrate formulations: Alternatives for the diagnosis of insulin dysregulation in horses?

Article

Full-text available

Jan 2023
J VET INTERN MED

Background Oral glycemic challenge (GC) tests are recommended for diagnosis of insulin dysregulation (ID). Various protocols are used, but all have limitations in terms of palatability, ease of use, variable composition, geographic availability, or some combination of these. Hypothesis/Objective To evaluate newly developed formulations with defined carbohydrate composition for use as oral GCs. Animals Thirty‐four horses and ponies in various metabolic states. Methods Our objectives were carried out in 2 separate cross‐over experiments. First, the palatability and acceptance of various GCs (2 syrups, 1 granulate) offered for free intake were compared to glucose mixed in a chaff‐based diet. Subsequently, syrups were administered by syringe and compared to an oral glucose test using naso‐gastric tubing (tube OGT) to investigate the glycemic and insulinemic responses. Second, these variables were compared in the best performing GC‐formulations (granulate further optimized to pelleted formulation and 1 syrup) and a tube OGT. All GCs were administered with equivalent amounts of 0.5 g glycemic carbohydrates per kg body weight. Results Only the GC pellets were consumed completely by all horses (consumption time 5 ± 2 min). When administered by syringe, the GC syrup also was well accepted. The insulin concentrations at 120 min correlated significantly between tube OGT and GC pellets (r = .717; P < .001) or GC syrup (r = .913; P < .001). The new GC syrup and GC pellets discriminate between healthy and ID horses. Conclusions and Clinical Significance The GC pellets (DysChEq)™ and GC syrup can be used as palatable and well‐accepted oral GC tests for assessment of ID in horses.

Pituitary Pars Intermedia Dysfunction (PPID) in Horses

Article

Full-text available

Oct 2022

Simple Summary Pituitary pars intermedia dysfunction is the most common endocrine disease of geriatric horses and affects quality of life, immunocompetence and athletic performance. Clinical signs of pituitary pars intermedia dysfunction can include hypertrichosis (a long hair coat), muscle atrophy, a pendulous abdomen, recurrent infections, lethargy, lameness, polydipsia, and polyuria (drinking and urinating more than normal). Awareness of endocrine diseases such as pituitary pars intermedia dysfunction in the equine community has increased in the recent years, and new research is becoming available providing insight into prevalence of clinical signs, difficulties with current diagnostic techniques, and treatment of the condition. The purpose of this article is to review the current literature, to provide veterinarians access to current perspectives for pathophysiology, clinical signs, diagnosis, and treatment of pituitary pars intermedia dysfunction. Abstract Substantial morbidity results from pituitary pars intermedia dysfunction (PPID) which is often underestimated by owners and veterinarians. Clinical signs, pathophysiology, diagnostic tests, and treatment protocols of this condition are reviewed. The importance of improved recognition of early clinical signs and diagnosis are highlighted, as initiation of treatment will result in improved quality of life. Future research should be targeted at improving the accuracy of the diagnosis of PPID, as basal adrenocorticotropic hormone (ACTH) concentration can lack sensitivity and thyrotropin releasing hormone (TRH) used to assess ACTH response to TRH stimulation is not commercially available as a sterile registered product in many countries. The relationship between PPID and insulin dysregulation and its association with laminitis, as well as additional management practices and long-term responses to treatment with pergolide also require further investigation.

Associations of plasma sphingolipid profiles with insulin response during oral glucose testing in Icelandic horses

Article

Full-text available

Jun 2021
J VET INTERN MED

Background Sphingolipids modulate insulin sensitivity in mammals. Increased synthesis of ceramides is linked to decreased insulin sensitivity of tissues. Conversely, activation of the insulin signaling pathway can downregulate ceramide synthesis. Elucidating the association between sphingolipid metabolism and insulin response during oral glucose testing may help explain the pathophysiology of insulin dysregulation in horses. Hypotheses Horses with insulin dysregulation will have a plasma sphingolipid profile characterized by increased ceramide concentrations. The plasma sphingolipid profile will have decreased ceramide concentrations after acute activation of the insulin signaling pathway by oral glucose testing. Animals Twelve Icelandic horses. Methods Horses were subjected to an oral glucose test (0.5 g/kg body weight glucose), with plasma insulin concentrations measured at 0, 30, 60, 120, 180, and 240 minutes postglucose administration. Plasma samples were collected at 0 and 120 minutes for sphingolipid profiling using a liquid chromatography‐mass spectrometry‐based metabolomics analysis. Eighty‐three species of sphingolipids were detected, including 3‐ketosphinganines, dihydroceramides, ceramides, dihydrosphingomyelins, sphingomyelins, galatosylceramides, glucosylceramides, lactosylceramides, and ceramide‐1‐phosphates. Results Glucose administration did not significantly alter plasma sphingolipid profiles. C22:0‐ceramide, C24:1‐ceramide, C23:0‐ceramide, C16:1‐sphingomyelin, C22:0‐dihydroceramide, and C24:0‐ceramide were positively correlated with the insulin response (area under the curve). Conclusion and Clinical Importance Positive correlation between the insulin response and sphingolipid concentrations implies upregulated sphingolipid metabolism in insulin dysregulated horses. A high plasma ceramide concentration can indicate insulin dysregulation in horses.

The application of a new laminitis scoring method to model the rate and pattern of improvement from equine endocrinopathic laminitis in a clinical setting

Article

Full-text available

Jan 2021
BMC Vet Res

Background Endocrinopathic, or hyperinsulinaemia-associated laminitis (HAL) is a common and debilitating equine foot disease, and although no pharmacological treatments are registered, several are under development. To evaluate the effect of such treatments, an accurate and consistent method is needed to track the clinical signs of laminitis over time, and the natural history of the disease, in terms of a ‘normal’ pattern of improvement, needs to be understood. This study examined the improvement pattern in clinical cases of naturally-occurring HAL subjected to a range of best-practice interventions, using two different scoring methods. Eighty horses and ponies with suspected HAL were enrolled in a study conducted at 16 veterinary practices across Germany. The severity of laminitis was assessed by independent veterinarians using both the traditional Obel method and a modified Obel method developed by Meier and colleagues. Assessments were made on the day of diagnosis (d 0), then on days 4, 9, 14, 25 and 42 during the intervention period. Pain medications were withheld for 24 h prior to clinical examination in all cases. Results Time to marked improvement from laminitis varied between individuals, but was difficult to monitor accurately using the Obel method, with the median grade being 2/4 on days 0 and 4, then 0/4 from d 9 onwards. More subtle changes could be identified using the Meier method, however, and the median scores were seen to follow the form of an exponential decay model in most horses, improving from 8/12 on d 0, to 0/12 on d 25. Within this composite scoring method, considerable variation was observed in the rate of improvement of individual clinical signs, with the average time taken for each sign to reach a median score of 0 ranging from 4 days (foot lift and weight shifting) to 25 days (gait when turned in a circle) across all 80 horses. Conclusions The Meier method provides a reliable and consistent method for monitoring the clinical status of horses with HAL, and despite the variability, the pattern of improvement described here should provide a useful benchmark against which individual cases and new treatments can be assessed.

Metabolic changes induced by oral glucose tests in horses and their diagnostic use

Article

Full-text available

Dec 2020
J VET INTERN MED

Background Little is known about the implications of hyperinsulinemia on energy metabolism, and such knowledge might help understand the pathophysiology of insulin dysregulation. Objectives Describe differences in the metabolic response to an oral glucose test, depending on the magnitude of the insulin response. Animals Twelve Icelandic horses in various metabolic states. Methods Horses were subjected to 3 oral glucose tests (OGT; 0.5 g/kg body weight glucose). Basal, 120 and 180 minutes samples were analyzed using a combined liquid chromatography tandem mass spectrometry and flow injection analysis tandem mass spectrometry metabolomic assay. Insulin concentrations were measured using an ELISA. Analysis was performed using linear models and partial least‐squares regression. Results The kynurenine : tryptophan ratio increased over time during the OGT (adjusted P‐value = .001). A high insulin response was associated with lower arginine (adjusted P‐value = .02) and carnitine (adjusted P‐value = .03) concentrations. A predictive model using only baseline samples performed well with as few as 7 distinct metabolites (sensitivity, 86%; 95% confidence interval [CI], 81%‐90%; specificity, 88%; 95% CI, 84%‐92%). Conclusions and Clinical Importance Our results suggest induction of low‐grade inflammation during the OGT. Plasma arginine and carnitine concentrations were lower in horses with high insulin response and could constitute potential therapeutic targets. Development of screening tools to identify insulin‐dysregulated horses using only baseline blood sample appears promising.

Continuous glucose measurement (CGM) in the horse -A field trial

Conference Paper

Full-text available

May 2025

Konstanze Rasch

The technology for continuous glucose monitoring in the form of self-adjusting sensors has been on the market for the better part of a decade. Continuous glucose monitoring (CGM) has also found its way into veterinary practices in order to improve the treatment of diabetic dogs and cats. It has not been used on horses just yet. Initial studies have been conducted in the field of monitoring patients in intensive care and in the field of science to evaluate and standardize interstitial glucose monitoring systems for equine research. We wanted to test whether and under what conditions and prerequisites continuous glucose measurement in horses with the FreeStyle Libre 3 sensor is a practical method for identifying and monitoring insulin dysregulated horses. In the field trial, five horses were to be continuously monitored over a period of one week using the "FreeStyle Libre 3" tissue glucose sensor from Abbott. The subjects were smaller horses and ponies of varying sizes and ages. Three of the ponies suffered from chronic laminitis and have had a long history of laminitis. The continuous glucose monitoring in horses using CGM sensors from human medicine can be a very useful tool. It can be used to sample insulin dysregulated horses and – with more knowledge and experience with the technology – it can certainly also to identify insulin dysregulated horses in the future. And, in our view, it is useful for checking and adapting feed management for such horses. The sensors are stress-free to apply and relatively inexpensive. The measurement accuracy is good and monitoring is comparatively easy to carry out.

Dexamethasone administration transiently increases insulin response to an oral carbohydrate challenge in horses

Article

Full-text available

Feb 2025
AM J VET RES

Objective Dexamethasone is used to experimentally induce insulin resistance; however, its impact on insulin secretion is unclear. This study aimed to assess the responses to oral carbohydrate challenges in dexamethasone-treated horses. Methods 8 healthy Standardbreds received 0.08 mg/kg of dexamethasone IM every 48 hours for 14 days in June 2022 (winter in the Southern hemisphere). Oral glucose tests (OGT) were conducted before treatment (day 1) and on days 8 and 15. Glucose, insulin, triglycerides, total and active glucagon-like peptide-1 (tGLP-1 and aGLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were measured at baseline and at intervals up to 240 minutes after OGT. The results were analyzed using a mixed-effects linear regression model. Results After 8 days of dexamethasone, significant increases in areas under the curve (AUC) of glucose (effect size, +139.1 [95% CI, 124.0 to 154.1] mg/dL·min), insulin (+297.6 [95% CI, 214.6 to 380.8] µIU/mL·min), triglycerides (+4,854.3 [95% CI, 2,181.3 to 7,527.3] mg/dL·min), tGLP-1 (+2.58 [95% CI, 0.23 to 4.93] pmol/L·min), and GIP (+65.56 [95% CI, 40.98 to 90.16] pg/mL·min) were detected post-OGT. These effects were blunted by day 15, with glucose, insulin, and active glucagon-like peptide-1 AUC significantly lower than on day 8 and tGLP-1, triglycerides, and GIP AUC not different from day 1. No horse developed clinical laminitis. Conclusions Dexamethasone increased insulin secretion after an OGT with higher lipid mobilization and stimulation of the enteroinsular axis, but the effect was partially reversed by day 15. Clinical Relevance While dexamethasone induces insulin resistance consistently over prolonged periods, its effect on insulin secretion seems transient.

Focus on the epidemiology, pathophysiology, diagnosis, and management of insulin dysregulation in horses

Article

Feb 2024

Because there are various inter-related disorders of insulin metabolism that all may contribute to the final result of hyperinsulinaemia, the phrase "insulin dysregulation" has become the most acceptable term to use when describing equine metabolic syndrome (EMS). Insulin dysregulation is widespread in horses, and it appears to be more prevalent in physically sedentary horses. Laminitis and hyperinsulinaemia have been linked, as have other components of insulin dysregulation. Diagnosis of insulin dysregulation should be done in stages, beginning with basal testing, which includes baseline values of insulin and glucose, and concluding with dynamic tests, which detect tissue insulin resistance and hyperinsulinaemia. Dietary adjustments are the key to weight loss in the majority of EMS horses. To encourage weight loss, the horse should be given around 1.25% of its body weight every day. Exercise not only aids equid weight loss but also improves insulin sensitivity. The exercise should be tailored to the specific horse, taking into account its breed, fitness level, and owner's resources. When an obese horse is unable to exercise owing to laminitis or when obesity persists after extensive exercise and dietary management, levothyroxine sodium and metformin hydrochloride can be given to help accelerate weight loss and increase insulin sensitivity. Insulin dysregulation is a defining feature of equine metabolic syndrome and has garnered attention due to its direct link to laminitis. There is need for an in-depth understanding of ID in order to prevent the development of clinical laminitis. The current study discusses the epidemiology, pathophysiology, diagnosis, and management of insulin dysregulation in horses.

A glucagon-like peptide-1 receptor antagonist reduces the insulin response to a glycemic meal in ponies

Article

Full-text available

Dec 2023
J ANIM SCI

High plasma concentrations of insulin can cause acute laminitis. Ponies and horses with insulin dysregulation (ID) exhibit marked hyperinsulinaemia in response to dietary hydrolysable carbohydrates. Glucagon-like peptide-1 (GLP-1), an incretin hormone released from the gastrointestinal tract, enhances insulin release, and is increased post-prandially in ponies with ID. The aim of this study was to determine whether blocking the GLP-1 receptor reduces the insulin response to a high glycaemic meal. Five adult ponies were adapted to a cereal meal then given two feed challenges 24 h apart of a meal containing 3 g/kg BW micronized maize. Using a randomised cross-over design all ponies received both treatments, where one of the feeds was preceded by the IV administration of a GLP-1 receptor blocking peptide, Exendin-3 (9-39) amide (80 µg/kg), and the other feed by a sham treatment of peptide diluent only. Blood samples were taken before feeding and peptide administration, and then at 30 min intervals via a jugular catheter for 6 hours for the measurement of insulin, glucose and active GLP-1. The peptide and meal challenge caused no adverse effects, and the change in plasma glucose in response to the meal was not affected (P = 0.36) by treatment: peak concentration 9.24 ± 1.22 and 9.14 ± 1.08 mmol/L without and with the antagonist, respectively. Similarly, there was no effect (P = 0.35) on plasma active GLP-1 concentrations: peak concentration 14.3 ± 1.36 pM and 13.7 ± 1.97 pM without and with the antagonist, respectively. However, the antagonist caused a significant decrease in the area under the curve for insulin (P = 0.04), and weak evidence (P = 0.06) of a reduction in peak insulin concentration (456 ± 147 μIU/mL and 370 ± 146 μIU/mL without and with the antagonist, respectively). The lower overall insulin response to the maize meal after treatment with the antagonist demonstrates that blocking the GLP-1 receptor partially reduced insulin production in response to a high starch, high glycaemic index, diet. Using a different methodological approach to published studies, this study also confirmed that GLP-1 does contribute to the excessive insulin production in ponies with ID.

Obesity and obesity‐associated metabolic disease conditions in Connemara ponies in Ireland

Article

Full-text available

Nov 2023
EQUINE VET J

Background Equine obesity combined with insulin dysregulation (ID) is a major risk factor associated with laminitis. Some pony breeds appear to be at increased risk. However, little is known regarding the prevalence of obesity or hyperinsulinaemia as evidence of ID in Irish ponies. Objective To investigate the prevalence of obesity and associated endocrine/metabolic disease conditions in Connemara ponies and to determine if hyperinsulinaemia in these ponies could be predicted by morphometric or metabolic markers. Study design Cross‐sectional study. Methods The study population included registered Connemara ponies recruited through public and veterinary social media posts. Ponies underwent a physical examination and information on their management and clinical history was obtained via owner questionnaire. The body condition score (BCS) was measured using the Henneke system; cresty neck score (CNS) and regionalised adiposity were also assessed. Hyperinsulinaemia was confirmed by measuring serum basal insulin concentration (BIC) or insulin concentration after an oral sugar test (OST). Blood glucose and triglyceride concentrations were measured. Characteristics of hyperinsulinaemic and insulin‐sensitive ponies were compared by logistic regression. Results Two hundred ponies were included; 59 ponies (29.5%) had a BCS ≥7, 58 (29.0%) had a CNS ≥2.5 and 135 (67.5%) had regionalised adiposity; 137 (68.5%) ponies had at least one of these abnormalities. Owner‐reported history or clinical evidence of chronic laminitis was found in 92 ponies (46.0%). Hyperinsulinaemia was confirmed in 32 ponies (16.0%), including 23 of 91 (25.3%) detected by OST and 9 of 109 (8.3%) by BIC. Hypertriglyceridaemia was observed in 12 of 198 ponies (6.1%) ponies and hyperglycaemia in 11 of 197 ponies (5.6%) ponies. The odds of hyperinsulinaemia increased by a factor of 6.53 (95% confidence interval: 2.95, 15.21) when BCS was ≥7. Main limitations The OST was not performed in all ponies. Conclusions Increased adiposity, laminitis and metabolic derangements are prevalent in this native Irish pony breed.

BEVA primary care clinical guidelines: Diagnosis and management of equine pituitary pars intermedia dysfunction

Article

Full-text available

Oct 2023
EQUINE VET J

Background Pituitary pars intermedia dysfunction (PPID) is a prevalent, age‐related chronic disorder in equids. Diagnosis of PPID can be challenging because of its broad spectrum of clinical presentations and disparate published diagnostic criteria, and there are limited available treatment options. Objectives To develop evidence‐based primary care guidelines for the diagnosis and treatment of equine PPID based on the available literature. Study design Evidence‐based clinical guideline using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. Methods Research questions were proposed by a panel of veterinarians and developed into PICO or another structured format. VetSRev and Veterinary Evidence were searched for evidence summaries, and systematic searches of the NCBI PubMed and CAB Direct databases were conducted using keyword searches in July 2022 and updated in January 2023. The evidence was evaluated using the GRADE framework. Results and recommendations The research questions were categorised into four areas: (A) Case selection for diagnostic testing, pre‐test probability and diagnostic test accuracy, (B) interpretation of test results, (C) pharmacological treatments and other treatment/management options and (D) monitoring treated cases. Relevant veterinary publications were identified and assessed using the GRADE criteria. The results were developed into recommendations: (A) Case selection for diagnostic testing and diagnostic test accuracy: (i) The prevalence of PPID in equids aged ≥15 years is between 21% and 27%; (ii) hypertrichosis or delayed/incomplete hair coat shedding provides a high index of clinical suspicion for PPID; (iii) the combination of clinical signs and age informs the index of clinical suspicion prior to diagnostic testing; (iv) estimated pre‐test probability of PPID should be considered in interpretation of diagnostic test results; (v) pre‐test probability of PPID is low in equids aged <10 years; (vi) both pre‐test probability of disease and season of testing have strong influence on the ability to diagnose PPID using basal adrenocorticotropic hormone (ACTH) or ACTH after thyrotropin‐releasing hormone (TRH) stimulation. The overall diagnostic accuracy of basal ACTH concentrations for diagnosing PPID ranged between 88% and 92% in the autumn and 70% and 86% in the non‐autumn, depending on the pre‐test probability. Based on a single study, the overall diagnostic accuracy of ACTH concentrations in response to TRH after 30 minutes for diagnosing PPID ranged between 92% and 98% in the autumn and 90% and 94% in the non‐autumn, depending on the pre‐test probability. Thus, it should be remembered that the risk of a false positive result increases in situations where there is a low pre‐test probability, which could mean that treatment is initiated for PPID without checking for a more likely alternative diagnosis. This could compromise horse welfare due to the commencement of lifelong therapy and/or failing to identify and treat an alternative potentially life‐threatening condition. (B) Interpretation of diagnostic tests: (i) There is a significant effect of breed on plasma ACTH concentration, particularly in the autumn with markedly higher ACTH concentrations in some but not all ‘thrifty’ breeds; (ii) basal and/or post‐TRH ACTH concentrations may also be affected by latitude/location, diet/feeding, coat colour, critical illness and trailer transport; (iii) mild pain is unlikely to have a large effect on basal ACTH, but caution may be required for more severe pain; (iv) determining diagnostic thresholds that allow for all possible contributory factors is not practical; therefore, the use of equivocal ranges is supported; (v) dynamic insulin testing and TRH stimulation testing may be combined, but TRH stimulation testing should not immediately follow an oral sugar test; (vi) equids with PPID and hyperinsulinaemia appear to be at higher risk of laminitis, but ACTH is not an independent predictor of laminitis risk. (C) Pharmacologic treatments and other treatment/management options: (i) Pergolide improves most clinical signs associated with PPID in the majority of affected animals; (ii) Pergolide treatment lowers basal ACTH concentrations and improves the ACTH response to TRH in many animals, but measures of insulin dysregulation (ID) are not altered in most cases; (iii) chasteberry has no effect on ACTH concentrations and there is no benefit to adding chasteberry to pergolide therapy; (iv) combination of cyproheptadine with pergolide is not superior to pergolide alone; (v) there is no evidence that pergolide has adverse cardiac effects in horses; (vi) Pergolide does not affect insulin sensitivity. (D) Monitoring pergolide‐treated cases: (i) Hormone assays provide a crude indication of pituitary control in response to pergolide therapy, however it is unknown whether monitoring of ACTH concentrations and titrating of pergolide doses accordingly is associated with improved endocrinological or clinical outcome; (ii) it is unknown whether monitoring the ACTH response to TRH or clinical signs is associated with an improved outcome; (iii) there is very weak evidence to suggest that increasing pergolide dose in autumn months may be beneficial; (iv) there is little advantage in waiting for more than a month to perform follow‐up endocrine testing following initiation of pergolide therapy; there may be merit in performing repeat tests sooner; (v) timing of sampling in relation to pergolide dosing does not confound measurement of ACTH concentration; (vi) there is no evidence that making changes after interpretation of ACTH concentrations measured at certain times of the year is associated with improved outcomes; (vii) evidence is very limited, however, compliance with PPID treatment appears to be poor and it is unclear whether this influences clinical outcome; (viii) evidence is very limited, but horses with clinical signs of PPID are likely to shed more nematode eggs than horses without clinical signs of PPID; it is unclear whether this results in an increased risk of parasitic disease or whether there is a need for more frequent assessment of faecal worm egg counts. Main limitations Limited relevant publications in the veterinary scientific literature. Conclusions These findings should be used to inform decision‐making in equine primary care practice.

The effect of pre‐dosing with metformin on the insulin response to oral sugar in insulin‐dysregulated horses

Article

Full-text available

Aug 2023
EQUINE VET J

Background A single dose of metformin administered 1 h prior to oral glucose challenge was previously shown to reduce insulinaemic responses in horses with experimentally‐induced insulin dysregulation (ID). Targeted administration could be useful for controlling post‐prandial hyperinsulinaemia in horses with naturally‐occurring ID. Objectives The objective was to compare the insulinaemic and glycaemic responses to oral sugar testing (OST) performed at different intervals after a single dose of metformin in horses with naturally‐occurring ID. We hypothesised that pre‐treatment with one dose of metformin would significantly decrease the insulinaemic response to OST. Study design Randomised cross‐over in vivo experiment. Methods Eight university‐owned adult horses with naturally‐occurring ID underwent OST 1, 2 and 6 h following a single oral dose of metformin (30 mg/kg) or 1 h after placebo (240 mL water) with a 7‐day washout between treatments over a period of 3 weeks. Plasma insulin, C‐peptide and glucose concentrations were measured at 0, 60 and 90 min after 0.45 mL/kg light corn syrup and the effect of treatment (and the interval since dosing) examined using a mixed effects linear regression model. Results Metformin treatment had no significant effect on plasma glucose, insulin or C‐peptide concentrations at any time point compared with placebo (p > 0.05). For OST 1 h post metformin, median (IQR) plasma insulin was 91.3 (62.4–114.9) μIU/mL at 60 min versus 76.2 (59.1–134.5) for placebo (p = 0.8) and 62.7 (31.4–109.7) at 90 min versus 51.8 (29.2–126.3) for placebo (p = 0.9). Main limitations Small sample size may limit identification of more subtle decreases in insulin concentration with metformin pre‐dosing. The results of this study are relevant only for one pre‐treatment dose (30 mg/kg) which limits extrapolation to predictions about the effects of longer‐term metformin administration on insulin and glucose dynamics in the horse. Conclusions and clinical importance The results do not support the use of targeted metformin treatment to reduce post‐prandial hyperinsulinaemia in horses with naturally‐occurring ID.

Equine metabolic syndrome: evolution of understanding over two decades: a personal perspective

Article

Full-text available

Nov 2020

There has been a marked increase in the incidence of equine obesity globally, especially in countries where there has been a shift away from the horse having an economically essential working role. This change in its core role, plus the increasing numbers of individual horse owners without access to traditional knowledge of animal and land management, have helped fuel this equine obesity ‘epidemic’. Other important potential contributory factors include increased availability of good grazing and/or forage, as well as supplementary feeds. Obesity now presents a major welfare issue for horses and ponies, not only because of the direct weight-associated effects, but also due to the increased risk it poses for certain clinical conditions, in particular laminitis. For many owners and veterinarians, obesity and the equine metabolic syndrome are synonymous, but this is not necessarily the case. Furthermore, as we understand more about this syndrome and the causes of endocrinopathic laminitis, the emphasis has shifted from tissue or peripheral insulin resistance to insulin dysregulation. The present paper outlines how our knowledge of equine metabolic syndrome arose and continues to develop, as well as the authors’ personal involvement in some of these advances.

Current understanding of insulin dysregulation and its relationship with carbohydrate and protein metabolism in horses

Article

Mar 2025
DOMEST ANIM ENDOCRIN

Pasture-related diseases and disorders

Chapter

Jan 2025

Insulin resistance versus dysregulation—a distinction without a difference

Article

Dec 2024

Eleanor Kellon

For the last 10 years, the term ‘insulin dysregulation’ has replaced ‘insulin resistance’ when referring to horses with hyperinsulinaemia. The rationale was that this was an all‐inclusive term that covered all possible causes of hyperinsulinaemia. The implication is that hyperinsulinaemia has been shown to occur outside of insulin resistance; with insulin resistance being defined as failure of the insulin‐sensitive cells to respond normally to insulin, as best documented by the euglycaemic hyperinsulinaemic clamp. This article will show the evidence for that is weak to nonexistent in the horse and the term ‘insulin dysregulation’ is a misnomer that should be abandoned.

Equine metabolic syndrome: part 2

Article

Jul 2024

Philip J. Johnson

Obesity, insulin dysregulation and predisposition to endocrinopathic laminitis represent the major cornerstones of equine metabolic syndrome. This article summarises new information pertaining to the predispositions and pathophysiology of equine metabolic syndrome and presents some newly emergent and effective treatments for this important and common condition.

Evaluating insulindysregulation in horses: A two-step insulin-tolerance test using porcine zinc insulin

Article

Jun 2024
VET J

Métodos diagnósticos da Síndrome Metabólica Equina (SME): Revisão de Literatura

Article

Full-text available

Jan 2023

Understanding, diagnosing and managing endocrinopathic laminitis

Article

Jan 2024

Nora S. Grenager

Endocrinopathic laminitis (or hyperinsulinaemia-associated laminitis) is the most common type of laminitis encountered in equine practice. Strict attention to risk factors and early recognition and diagnosis of insulin dysregulation – as part of equine metabolic syndrome or pituitary pars intermedia dysfunction – greatly decreases the risk of hyperinsulinaemia-associated laminitis. Early treatment and a committed client, veterinary and farriery team is critical to improve the prognosis. Treatment of hyperinsulinaemia-associated laminitis should encompass a three-pronged approach: treat the underlying cause (insulin dysregulation associated with equine metabolic syndrome or pituitary pars intermedia dysfunction); give anti-inflammatories and analgesics; biomechanically support the foot. The field of equine endocrinopathic disease is very active, so it is important to stay up to date on potential diagnostics and therapeutics.

A practical approach to hyperinsulinaemia in horses with equine metabolic syndrome

Article

Jan 2024
EQUINE VET EDUC

Laminitis associated with hyperinsulinaemia is a significant cause of morbidity and mortality in horses with equine metabolic syndrome. The diagnosis and management of hyperinsulinaemia are therefore critical to prevent the development of laminitis. This review article aims to help primary care clinicians manage patients with hyperinsulinaemia by providing an overview of diagnostics, management strategies and new therapies that are available.

Insulin Dysregulated Horses Metabolic Responses to Forage Pellets

Article

Dec 2023
J EQUINE VET SCI

Deciphering reference intervals and clinical decision limits in equine endocrine diagnostic testing

Article

Oct 2023
VET J

Diagnosis of equine endocrinopathies: The value of measuring blood glucose during an oral glucose test

Article

Sep 2023
VET J

Causas da Síndrome Metabólica Equina (SME): Revisão de Literatura

Article

Full-text available

Jan 2023

Evaluation of field-testing protocols to diagnose insulin dysregulation in ponies using a Bayesian approach

Article

Aug 2023
VET J

Field tests and their association with laminitis have not been evaluated in large cohorts. The objectives of this study were to evaluate the performance of basal insulin (BI), the oral sugar test (OST) and the insulin tolerance test (ITT) to diagnose ID and investigate their association with laminitis. Insulin dysregulation status was determined in 146 ponies using BI (insulin concentration >20 µIU/mL), an OST (insulin concentration >65 µIU/mL at 60 or 90min after oral administration of 0.45mL/kg corn syrup) and an ITT (< 50% reduction in glucose concentration 30min after intravenous administration of 0.1 IU/kg insulin). Laminitis was identified using modified-Obel scores. A Bayesian approach was used to define the characteristics of the tests and receiver operating characteristic curves were used to assess their association with laminitis. All tests were well tolerated and laminitis was diagnosed in 9% of ponies. Insulin dysregulation was diagnosed in 15% of ponies using BI, 38% using the OST and 54% using the ITT with 11% of ponies positive for all 3 tests. The sensitivities and specificities of BI, the OST and the ITT to diagnose ID were 0.52 (95% confidence interval [CI], 0.35 - 0.79) and 0.97 (95% CI, 0.91 - 1.00), 0.84 (95% CI, 0.70 - 0.94) and 0.60 (95% CI, 0.49 - 0.71), and 0.85 (95% CI, 0.68 - 0.96) and 0.88 (95% CI, 0.75 - 0.97), respectively. Only BI and the OST were associated with laminitis (P = 0.003 and 0.015, respectively).

Equine Endocrine Disease: Challenges With Case Definition for Research

Article

May 2023
J EQUINE VET SCI

Equine endocrine disease is an important area for equine research, requiring an appropriate case definition for inclusion and criteria for exclusion from disease. Defining a case for research may be different from criteria for clinical diagnosis. Further, clinical diagnosis recommendations have been changing regularly, making this area challenging for equine scientists. This review discusses the diagnosis of major equine endocrine diseases, pituitary pars intermedia dysfunction, equine metabolic syndrome and insulin dysregulation, focusing on the most appropriate diagnostic methods for research case definitions. Different diagnostic methods, including use of reference intervals and clinical decision limits, will be discussed with their relative merits for use in case definition for research.

Equine metabolic syndrome: Role of the enteroinsular axis in the insulin response to oral carbohydrate

Article

Feb 2023
VET J

Equine insulin dysregulation (ID) comprises amplified insulin responses to oral carbohydrates or insulin resistance, or both, which leads to sustained or periodic hyperinsulinaemia. Hyperinsulinaemia is important in horses because of its clear association with laminitis risk, and the gravity of this common sequela justifies the need for a better understanding of insulin and glucose homeostasis in this species. Post-prandial hyperinsulinaemia is the more commonly identified component of ID and is diagnosed using tests that include an assessment of the gastrointestinal tract (GIT). There are several factors present in the GIT that either directly, or indirectly, enhance insulin secretion from the endocrine pancreas, and these factors are collectively referred to as the enteroinsular axis (EIA). A role for key components of the EIA, such as the incretin peptides glucagon-like peptide-1 and 2, in the pathophysiology of ID has been investigated in horses. By comparison, the function (and even existence) of many EIA peptides of potential importance, such as glicentin and oxyntomodulin, remains unexplored. The incretins that have been examined all increase insulin responses to oral carbohydrate through one or more mechanisms. This review presents what is known about the EIA in horses, and discusses how it might contribute to ID, then compares this to current understanding derived from the extensive studies undertaken in other species. Future directions for research are discussed and knowledge gaps that should be prioritised are suggested.

A review of cellular and molecular mechanisms in endocrinopathic, sepsis‐related and supporting limb equine laminitis

Article

Full-text available

Mar 2023
EQUINE VET J

Equine laminitis has both fascinated and frustrated veterinary researchers and clinicians for many years. The recognition that many ponies suffering from pasture‐associated laminitis have an insulin‐dysregulated phenotype (endocrinopathic laminitis, EL) and that prolonged insulin and glucose infusions can experimentally induce laminar pathology and functional failure are seminal discoveries in this field. Researchers have studied the molecular basis for disease pathogenesis in models of EL, sepsis‐related laminitis and supporting limb laminitis and generated much data over the last 15 years. This review attempts to synthesise those data, drawing comparisons between models and naturally occurring laminitis. A hypothesis is proposed that the basal epithelial cell stress is a central event in each category of laminitis. Furthermore, in naturally occurring pasture‐associated laminitis, pathways that predominate in each type of laminitis contribute to laminar lamellar pathology to varying extents. Based on the molecular mechanisms determined in experimental models, interactions between these pathways are identified.

Association between insulin dysregulation and adrenocorticotropic hormone in aged horses and ponies with no clinical signs of pituitary pars intermedia dysfunction

Article

Full-text available

Jan 2023
EQUINE VET J

Background High concentrations of adrenocorticotropic hormone (ACTH) are used as an indicator of pituitary pars intermedia dysfunction (PPID), but other factors that may influence ACTH need to be understood, if diagnostic reference ranges for ACTH are to be used with confidence. Insulin dysregulation (ID) could be one such factor, as insulin affects pituitary hormones in other species. Objectives To test the hypothesis that a relationship exists between high insulin and high ACTH in aged (>15‐year‐old) animals with no clinical signs of PPID. Study design A cohort study. Methods Thirteen horses and eleven ponies (17–25 years‐old; mares and geldings) were clinically examined for signs of PPID in the spring (November 2020) and autumn (April 2021). On the same day, blood samples were taken before and 2 h after an oral glucose test (OGT). Concentrations of insulin, glucose, ACTH and cortisol were measured. Results There was no association between ACTH and cortisol. However, there was a positive linear correlation between ACTH and post‐OGT (insulin in the autumn (r = 0.427, p = 0.04). Two horses and six ponies had ACTH above the cut‐off value for PPID diagnosis, and of these eight animals, six also had insulin concentrations above the cut‐off value for ID. Main limitations The cohort was small and thyrotropin‐releasing hormone (TRH) stimulation tests were not performed. Conclusions In autumn, high ACTH was associated with ID, when no clinical signs of PPID were present. Because ACTH is used in PPID diagnosis, further work is required to understand this interaction.

Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse

Article

Full-text available

Jan 2023
EQUINE VET J

Background Identifying intake levels of nonstructural carbohydrates (NSCs) that limit the postprandial insulinaemic response in the insulin dysregulated (ID) horse may help reduce hyperinsulinaemia‐associated laminitis (HAL) risk. Objective To determine if ID horses have thresholds for pure sources of starch and sugar, above which there is an augmented insulin response. Study design Randomised crossover experiment. Methods Fourteen adult horses (6 ID and 8 noninsulin dysregulated, NID; matched for bodyweight) were randomly fed eight dietary treatments. Dietary treatments were formulated using a base of low‐nonstructural carbohydrate pellet (LNSC; 0.04 g of water‐soluble carbohydrates (WSCs)/kg bwt and 0.01 g of starch/kg bwt), to which pure sugar (dextrose) or starch (50:50 mix of waxy‐maize and oat starch powder) sources were titrated to create diets with increasing amounts of either WSC (0.06–0.17 g WSC/kg bwt), or starch (0.03–0.1 g starch/kg bwt). Horses were fed each dietary treatment at a rate of 1 g/kg bwt once over 12 weeks. Serial blood samples were collected pre‐ and up to 240 min postprandially. Insulin was determined via RIA and diet analytes were determined via wet chemistry. Statistical analysis was performed with a mixed effect model. Positive incremental area under the curve for insulin (IAUCi) was calculated for all horses and dietary treatments. Results There was no significant effect of diet in NID horses but diets with NSC >0.1 g/kg bwt produced an augmented response in ID horses compared with the LNSC (p < 0.05). ID horses IAUCi were also significantly different to all NID IAUCi for diets with NSC >0.1 g/kg (p < 0.04). Apparent thresholds for sugar and starch addition varied. Conclusions Based on this study, using supplemental pure starch and sugar sources, ID horses seem to have an apparent threshold for NSC of around 0.1 g/kg bwt/meal, above which significantly increased insulin responses are seen compared with NID horses.

Preliminary observations on the use of ertugliflozin in the management of hyperinsulinaemia and laminitis in 51 horses: A case series

Article

Nov 2022
EQUINE VET EDUC

Background Hyperinsulinaemia‐associated laminitis (HAL) is encountered commonly in equine practice. There are currently no registered medications which specifically target hyperinsulinaemia in horses and ponies. Sodium–glucose cotransporter 2 inhibitors (SGLT2i) have been demonstrated to limit post‐prandial insulin responses and prevent the development of diet‐induced laminitis. Objectives The objective of the study was to evaluate the efficacy of an SGLT2i, ertugliflozin, in the management of hyperinsulinaemia and laminitis. Study design Retrospective case series. Methods Medical records of 51 horses and ponies that had presented with laminitis and hyperinsulinaemia and had been treated with oral ertugliflozin at 0.05 mg/kg once daily for a minimum of 30 days were reviewed. Results After 30 days of treatment with ertugliflozin, there was a reduction in insulin concentrations from a median of >300 μu/ml (IQR: 149, >300) to 43 μu/ml (IQR: 20, 66) ( p < 0.001). Modified Obel laminitis scores improved, reducing from a median of 10/12 to 1/12 ( p < 0.001). Median serum triglyceride concentrations increased from 0.6 (IQR: 0.4, 0.9) before treatment to 1.4 (IQR: 0.8, 3.7) mmol/L after 30 days of treatment ( p < 0.001) before declining, however, none of the horses developed any clinical signs of hyperlipaemia. Ten horses (19%) were reported to have polyuria and polydipsia during treatment, otherwise no adverse clinical effects were identified. Main limitations The study was limited by the absence of a control group, the retrospective data collection and the short period of follow‐up. Conclusions Ertugliflozin may be effective in reducing insulin concentrations in horses and ponies with equine metabolic syndrome and its use may hasten recovery from laminitis associated with hyperinsulinaemia.

Evaluation of peripheral blood polymorphonuclear cell functions after an oral carbohydrate overload in obese and insulin dysregulated horses

Article

Jun 2022
VET IMMUNOL IMMUNOP

Obesity and insulin dysregulation (ID) are increasingly prevalent conditions in equid populations worldwide. Immune impairment is well described in humans with metabolic dysfunction and is reported but still incompletely understood in horses. This study evaluated the effect of acute induced transient hyperglycemia on apoptosis, phagocytosis and oxidative burst activity of peripheral blood polymorphonuclear cells (PMN) of lean and obese adult horses with or without insulin dysregulation. Seventeen adult horses were allocated into three groups based on their body condition score (BCS) and metabolic status: lean-insulin sensitive (lean-IS), obese-insulin sensitive (obese-IS) and obese-insulin dysregulated (obese-ID). ID was determined by insulin tolerance testing (ITT). Blood glucose elevation was induced through an infeed-oral glucose test (in-feed OGT), and all assessments of PMN functions (apoptosis, phagocytosis and oxidative burst) were done in vitro after isolation from peripheral blood before and 120 min after carbohydrate overload. Results were analyzed using a repeated measures linear mixed model with significance defined at P<0.05. No differences in apoptosis were observed between experimental groups at any time point. Phagocytic capacity was significantly lower at baseline in the obese-ID group but increased in response to glucose administration when compared to the other two groups. Basal reactive oxygen species production in the obese-IS group differed significantly from the lean-IS and obese-ID groups and decreased significantly in response to glucose administration. Results from this study showed that both metabolic status itself, and oral glucose administration, seem to be factors that alter PMN functionality in horses, specifically phagocytosis and oxidative burst.

Diagnostic evaluation of insulin and glucose dynamics in light-breed horses receiving dexamethasone

Article

Full-text available

Jun 2022
CAN VET J

Objective: Insulin dysregulation is a hallmark of equine metabolic syndrome (EMS) and increases the risk for development of laminitis. Accurate diagnosis of insulin dysregulation is crucial for implementation of preventative strategies in this population. The objective was to assess the effects of dexamethasone administration on insulin and glucose dynamics in light-breed horses and assess the agreement of various diagnostic tests for insulin dysregulation [basal [insulin] (BI), oral sugar test (OST), and combined glucose-insulin test (CGIT)]. Animal: Fourteen adult light-breed horses. Procedure: Prospective, experimental study to assess insulin and glucose dynamics by performing basal insulin, OST, and CGIT before (baseline) and post-dexamethasone administration (0.08 mg/kg, PO, q24h) for 7 d. Insulin and glucose dynamics were assessed by the BI, OST, CGIT, and insulin sensitivity proxy measurements (RISQI, QUICKI, FGIR, HOMA-IR, IG) at the baseline and post-dexamethasone time points. Results: The OST area under the insulin and glucose curves were increased following dexamethasone treatment (P < 0.001 and P < 0.01, respectively). Basal insulin, OST [insulin] at 60 min and CGIT [insulin] at 45 min were increased at the post-dexamethasone time point (P < 0.001, < 0.001, and < 0.01). Similarly, time spent in the positive glucose phase during the CGIT was longer at the post-dexamethasone time point (P < 0.001). The proxy measurements for insulin sensitivity (RISQI, QUICKI, FGIR) were decreased (P < 0.01) and the proxy measurements for insulin resistance (HOMA-IR) and β-cell function (IG) were increased after dexamethasone administration (P < 0.01). More horses were classified with following dexamethasone administration, based on the diagnostic criteria for basal insulin (P = 0.03), OST (P = 0.01), and CGIT (P < 0.01). Kappa coefficients, measuring agreement between basal insulin, OST, and CGIT, showed none to moderate agreement at the baseline time point. Conclusion: Dexamethasone administration at 0.08 mg/kg, PO, q24h for 7 d worsened insulin dysregulation in adult light-breed horses based on findings of a basal insulin, OST, CGIT, and insulin sensitivity proxy measurements. There was none to moderate agreement between the basal insulin, OST, CGIT for the diagnosis of insulin dysregulation. Clinical relevance: Horses administered dexamethasone at a dose of 0.08 mg/kg, PO, q24h for 7 d should be considered insulin dysregulation and appropriate preventative strategies should be implemented. The variability of diagnostic performance of common tests for insulin dysregulation (basal insulin, OST, CGIT) may affect clinical decisions; therefore, performing multiple tests, including proxy measurements, may improve diagnostic accuracy of insulin dysregulation.

Seasonal Insulin Responses to the Oral Sugar Test in Healthy and Insulin Dysregulated Horses

Article

Apr 2022
J EQUINE VET SCI

Seasonal effects on the oral sugar test (OST), used to monitor insulin dysregulation (ID) status to help reduce laminitis risk, are poorly understood in the ID horse. Resting, (basal) insulin (T0) and 60-minute (T60) OST (0.15ml/Kg BW Karo Light Corn Syrup) insulin responses were evaluated, once per each season over 2yrs, in ID (n=11 14.9 ± 4.3 yrs.; mean ± SD) and non-insulin dysregulated (NID: n=11 16.4 ± 5.3 yrs.; mean ± SD) horses housed on the same farm. Seasonal morphometric measurements were collected: bodyweight (BW), body-condition scores (BCS), and cresty neck scores (CNS). Seasonal forage from paddocks and hay were collected and analyzed. Insulin was measured by RIA. Data were analyzed via Minitab Software 20.2 (mixed effects model). Season had no effect on BW(p=0.99); however, BCS and CNS were higher in ID vs NID in the spring, summer and fall (p<0.02). Paddock (p<0.05) but not hay (p>0.2) analytes varied across season. ID horses consistently had higher T0, T60 insulin concentrations vs NID (p<0.02). Season had no effect on NID T0 insulins (p=0.31), but T60 values were higher in the spring vs. summer (p=0.01). ID horses’ T0 & T60 insulins were higher in spring than fall and summer (p<0.01 & p<0.05) and winter T60 was higher than fall (p=0.04). ID horses changed their ID categorization across season, with T0 confirming ID status only 56% of the time whilst T60 confirmed 94% of the time. Therefore, regardless of seasonal changes, if the OST was used, ID diagnosis would be more consistent.

Advances in the understanding of laminitis and the role of nutrition in its management

Article

Jan 2022

Briony Witherow

Laminitis heavily impacts the equine population and, for this reason, has long been researched with respect to its prevention, causation, and management. Recent research has uncovered the importance of owner recognition in both the prevention and management of laminitis and highlighted this as a potential area for education. Furthermore, clearer definitions of the syndrome and its causation, along with risk of recurrence, should enable a more tailored approach to nutrition and feed management. Dissemination of current research into feeding practice should be seen as a key part of the ‘next steps’ in laminitis management and prevention. This review collates current recommendations with applications to practical feeding situations, and demonstrates that while there is information on what constitutes an appropriate diet ‘on paper’, the practicalities of providing this (particularly where forage is concerned), often represents a barrier to long-term use. It is in this area that future research should focus, to fully realise and benefit from the progress made to date.

Seasonal Insulin Responses to the Oral Sugar Test in Healthy and Insulin Dysregulated Horses

Article

Jan 2021

Endocrinopathic Laminitis

Article

Oct 2021
VET CLIN N AM-EQUINE

Nora S. Grenager

Endocrinopathic laminitis (EL) primarily occurs because of insulin dysregulation (ID) mediated through downstream effects of insulin on IGF-1R in lamellar tissues. There is likely contributing vascular and metabolic dysfunction within the lamellae, but EL is relatively non-inflammatory. EL is associated with lamellar stretching, proliferation, and failure, ultimately causing failure of the suspensory apparatus of the distal phalanx. Proper education regarding mitigating risk factors makes this a largely preventable cause of laminitis. Annual hoof evaluation plus screening geriatric horses for pituitary pars intermedia dysfunction and ID, and younger horses for ID, can significantly decrease the incidence of this devastating condition.

Effect of Dose and Fasting on Oral Sugar Test Responses in Insulin Dysregulated Horses

Article

Sep 2021
J EQUINE VET SCI

The oral sugar test (OST) is frequently used to identify insulin dysregulated (ID) equines. The effect of fasting and varying sugar dose for the OST has been investigated in the pony but little work has been done in the horse. This study aimed to investigate 1) an OST response with access to forage continued until the time of the OST or prevented for 3 hours prior to the OST and 2) responses of ID and non-insulin dysregulated (NID) horses to 2 different OST doses. Twenty-one mixed-breed horses (14.8 ± 3.2 years; 574.3 ± 83.3 kg) were used in two randomized crossover studies. Seven ID and 7 NID horses were used in study A, and 8 ID and 8 NID in study B. Study A horses underwent an OST (0.15 mL/kg BW) either after a fast (FA) or directly off pasture (FE). Study B horses received either a low (LD; 0.15 mL/kg BW) or high dose (HD; 0.45 mL/kg BW) OST on one occasion each. Blood was collected at basal (T0), and post-60 minute (T60) for later determination of insulin (RIA). Data were analyzed via ANOVA with repeated measures. ID horses had significantly (p<0.05) greater insulin responses than NID for all OSTs. There was no statistical difference between LD vs. HD mean insulin concentrations (T0, T60, delta insulin) for either ID or NID horses. ID had higher T0 (p<0.01) for FE compared to FA; however, FE and FA did not significantly affect T60 or delta insulins (DI) concentrations.

Endocrine and Metabolic Diseases

Chapter

Jan 2020

Laboratory Assessment of Lipid and Glucose Metabolism

Chapter

Jan 2021

Raquel M. Walton

Of the many lipids present in mammals, only a very few are of clinical and diagnostic relevance. This chapter discusses the primary lipid abnormalities encountered in equids and the methods for their diagnosis. Lipid hydrolysis produces fatty acids or complex alcohols that can combine with fatty acids to form esters. Hyperlipidemia and hyperlipemia are used synonymously to denote increases in serum or plasma lipid concentrations. The two principal lipids measured in animals are triglycerides and cholesterol. All triglycerides and the majority of cholesterol are carried within lipoproteins. Diagnosis of equine hyperlipidemia is dependent upon measurement of serum triglyceride concentration. In addition to lipids, the other principal component in energy metabolism in mammals is glucose. The chapter also provides information on diseases associated with glucose metabolic defects, including pasture laminitis, equine metabolic syndrome, pituitary pars intermedia dysfunction, and systemic inflammatory response syndrome.

Evaluation of a Chemiluminescent Immunoassay for Measurement of Equine Insulin

Article

Full-text available

Jan 2017
J VET INTERN MED

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.

Comparison of three different methods for the quantification of equine insulin

Article

Full-text available

Sep 2016
BMC Vet Res

Background: Exact analysis of equine insulin in blood samples is the key element for assessing insulin resistance or insulin dysregulation in horses. However, previous studies indicated marked differences in insulin concentrations obtained from sample analyses with different immunoassays. Most assays used in veterinary medicine are originally designed for use in human diagnostics and are based on antibodies directed against human insulin, although amino acid sequences between equine and human insulin differ. Species-specific assays are being used more frequently and seem to provide advantages compared to human-specific assays. The aim of this study was to compare three immunoassays, one porcine-specific insulin enzyme-linked immunosorbent assay (ELISA), advertised to be specific for equine insulin, one porcine-specific insulin radioimmunoassay (RIA) and one human-specific insulin chemiluminescence immunoassay (CLIA), all three widely used in veterinary laboratories for the analysis of equine insulin. Furthermore, we tested their clinical applicability in assessing insulin resistance and dysregulation by analysis of basal blood and blood samples obtained during a dynamic diagnostic stimulation test (OGT) with elevated insulin concentrations. Results: Insulin values obtained from the ELISA, RIA and CLIA, investigated for analyses of basal blood samples differed significantly between all three assays. Analyses of samples obtained during dynamic diagnostic stimulation testing with consecutively higher insulin concentrations revealed significantly (p < 0.001) lower insulin concentrations supplied by the CLIA compared to the ELISA. However, values measured by ELISA were intermediate and not different to those measured by RIA. Calculated recovery upon dilution, as a marker for assay accuracy in diluted samples, was 98 ± 4 % for ELISA, 160 ± 41 % for RIA and 101 ± 11 % for CLIA. Conclusions: Our results indicate that insulin concentrations of one sample measured by different methods vary greatly and should be interpreted carefully. Consideration of the immunoassay method and reliable assay-specific reference ranges are of particular importance especially in clinical cases where small changes in insulin levels can cause false classification in terms of insulin sensitivity of horses and ponies.

[Reference ranges of insulin, insulin like growth factor-1 and adrenocorticotropic hormone in ponies]

Article

Full-text available

Jan 2016

Objectives: The aim of this study was to validate a chemiluminescence immunometric assay using the IMMULITE 2000® for the determination of adrenocorticotropic hormone (ACTH), insulin and insulin-like growth factor-1 (IGF-1) from which reference ranges were calculated for ponies. Material and methods: Blood samples of 130 ponies aged 3-32 years were collected in the afternoon. The reference ranges were calculated according to the Guideline EP28-A3C of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) from 2010. Results: The determined intraday precision for insulin was 3.28%, for ACTH 3.35% and for IGF-1 1.84%. The interday precision (insulin: 3.45%; IGF-1: 2.89%; ACTH: 9.77%) was determined on three consecutive days, where the samples were stored at 4 °C. There was no significant loss of insulin activity nor of ACTH or IGF-1 concentration during this time. The reference ranges of insulin and IGF-1 (2.0-21.2 mU/l and 50.2-357.2 mU/l, respectively) were age independent, whereas for ACTH, an age-dependent reference range was established. Ponies aged 3-12 years had a significantly lower reference range (4.2-19.8 pg/ml) than ponies aged 13-32 years (5.0-22.6 pg/ml). Conclusion: The method used is suitable for the determination of ACTH, IGF-1 and insulin in serum of ponies, but the lowest detection limit for insulin is 2.0 mU/l. Clinical relevance: The calculated reference ranges of insulin and ACTH are helpful for the diagnosis and clinical monitoring of equine metabolic syndrome and pituitary pars intermedia dysfunction (PPID).

Equine hyperinsulinemia: Investigation of the enteroinsular axis during insulin dysregulation

Article

Full-text available

Nov 2015
AM J PHYSIOL-ENDOC M

Compared to other species insulin dysregulation in equids is poorly understood. Hyperinsulinemia causes laminitis, a significant and often lethal disease affecting the pedal bone/hoof wall attachment site. Until recently, hyperinsulinemia has been considered a counter-regulatory response to insulin resistance (IR), but there is growing evidence to support a gastrointestinal etiology. Incretin hormones released from the proximal intestine, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide, augment insulin secretion in several species, but require investigation in horses. This study investigated peripheral and gut-derived factors impacting insulin secretion by comparing the response to intravenous (IV) and oral D-glucose. Oral and IV tests were performed in 22 ponies previously shown to be insulin dysregulated, of which only 15 were classified as IR (IV test). In a more detailed study, nine different ponies received four treatments: D-glucose orally, D-glucose IV, oats and Workhorse-mix. Insulin, glucose and incretin concentrations were measured before and after each treatment. All nine ponies showed similar IV responses, but five were markedly hyper-responsive to oral D-glucose and four were not. Insulin responsiveness to oral D-glucose was strongly associated with blood glucose concentrations and oral glucose bioavailability, presumably driven by glucose absorption/distribution, as there was no difference in glucose clearance rates. Insulin was also positively associated with active GLP-1 following D-glucose and grain. This study has confirmed a functional enteroinsular axis in ponies which likely contributes to insulin dysregulation that may predispose them to laminitis. Further, IV tests for IR are not reliable predictors of the oral response to dietary non-structural carbohydrate.

Feeding and microbial disorders in horses: 1 - Effects of an abrupt incorporation of two levels of barley in a hay diet on microbial profile and activities

Article

Full-text available

Sep 2001
J EQUINE VET SCI

Cecal and colonic fluid samples collected from three ponies were analyzed to determine the effects of an abrupt incorporation of barley in a hay diet on their microbial and biochemical characteristics. Three diets based on meadow hay and rolled barley were tested in a 3×3 Latin square experiment: 100% hay (100:0, 114 gDM/KgBW0.75/day), 70% hay—30% barley (70:30, 69gDM/KgBW0.75/day) and 50% hay—50% barley (50:50, 58gDM/KgBW0.75/day). Enumeration of total anaerobic and aeroanaerobic bacteria, lactate-utilizing and cellulolytic bacteria, lactobacilli and streptococci, as well as pH, lactate and VFA concentrations, were determined before and five hours and 29 hours after the abrupt incorporation of barley in the hay diet. Whatever the amount of barley incorporated, an increase of total anaerobic bacteria, lactobacilli and streptococci, in the cecum and in the colon, was reported 29 hours after the changing of diet. Lactateutilizing and cellulolytic bacteria were not significantly modified five hours and 29 hours after the ingestion of a new diet. However a decrease of [(acetate+butyrate)/propionate] ratio was registered while lactate concentration increased although pH remained fairly constant through the changing of diet. The colon appeared to be the main site affected by the abrupt incorporation of readily fermentable carbohydrates in the diet. Thus, this section of the digestive tract needs further exploration to establish the linkage between the changes of the ecosystem as reported here, and the apparition of intestinal disorders.

Starch digestion in horses: The impact of feed processing

Article

Full-text available

Mar 2006
LIVEST SCI

Neither the partition of digestion between the foregut and the hindgut nor the factors of variation for diverse starches in feeds or rations is well documented in spite of their importance in respect of nutrition and health of the athletic horse. At similar intakes, feed processing and the botanical origin of the starch are two major factors that control the extent of prececal starch digestion. Physical and biochemical changes occurring during the process influence both the mean retention time of the feeds and the enzymatic activity in the foregut. Apparent digestibility of cereal starch varies from 20% to 90% in the foregut depending on the process used. Physical processes have a lesser effect than thermal and hydrothermal ones. Physical processes increase significantly the prececal digestibility of cornstarch but have a moderate impact on other cereals. Starch digestibility is increased by thermal and hydrothermal processes whatever the botanical origin. Feed processing was shown to affect the fermentability of starch in ruminants. In horses, a similar impact is expected not only in the hindgut but also in the stomach where numerous starch-utilizing bacteria have been observed. Further investigations are needed to identify the process which allows the highest prececal digestibility and decreases the hindgut fermentability of starch.

The repeatability of the Obel grading system for equine laminitis

Article

Full-text available

Jul 2010
VET REC

The aim of this study was to evaluate both the repeatability (intraobserver agreement) and reproducibility (interobserver agreement) of Obel grading, the most widely accepted method for describing the severity of equine laminitis. The study comprised two parts. In study A, to test intraobserver agreement, 25 ponies were graded twice by a single blinded experienced equine veterinary surgeon, on the first occasion via clinical examination and on the second occasion via a video recording of the initial clinical examination. In study B, to test interobserver agreement, video recordings of 13 ponies were graded independently by 58 blinded experienced equine veterinary surgeons. A weighted kappa (kappa(w)) statistic was used to determine the measure of agreement between gradings. Intraobserver agreement of Obel grading was shown to be moderate (kappa(w)=0.54), and interobserver agreement was found to be substantial (kappa(w)=0.65). In addition, intraobserver agreement improved from moderate to substantial (kappa(w) increased from 0.54 to 0.70) when the Obel grades were grouped and horses were categorised as either sound, or as having mild (grade 1 or 2) or severe (grade 3 or 4) lameness.

Prospective cohort study evaluating risk factors for the development of pasture-associated laminitis in the UK

Article

Jul 2016
EQUINE VET J

Background: Certain individuals appear predisposed to recurrent pasture-associated laminitis. Previous studies have predominantly investigated risk factors only after disease occurrence. Objectives: To investigate pasture-associated laminitis risk factors prior to disease occurrence. Study design: Prospective cohort study. Methods: Non-laminitic ponies >7 years old were recruited. Body condition score (BCS), height, weight, crest height and thickness were measured and an overnight dexamethasone suppression test performed. Plasma/serum adiponectin, leptin, triglyceride, basal insulin, insulin post dexamethasone, insulin-like growth factor (IGF)-1, IGF binding protein (IGFBP)-1, IGFBP-3, C-reactive protein, von Willebrand's factor (vWF), soluble (s) E-selectin and p-selectin concentrations were assayed. Follow-up was obtained from owners annually for 3 years to ascertain occurrence of veterinary-diagnosed pasture-associated laminitis. Data were analysed by multivariate logistic regression. ROC curves analysis was performed for significant risk factors and cut off values determined. Results: 446 animals were recruited; the median (interquartile range) age was 15 (10, 20) years; 50.4% were mares and 49.6% geldings; the most common breeds were Welsh (36%), Shetland (17%) and cob (9%); 72.2% were overweight/obese (BCS 7-9/9), 27.3% ideal weight (BCS 4-6/9) and 0.5% underweight (BCS 1-3/9). After 1, 2 and 3 years, 18 (4%), 30 (7%) and 44/446 (10%) animals had had laminitis. Plasma/serum [adiponectin], basal [insulin] and [insulin] post dexamethasone were significantly (p<0.05) associated with laminitis occurrence cumulatively after 1, 2 and 3 years. The accuracy to separate animals that did or did not develop laminitis determined using the area under the ROC curves was good (basal [insulin] after 1 year), fair (all others) or poor ([insulin] post dexamethasone). Main limitations: Animals were evaluated at a single time point and biomarkers were assayed using single assays. Conclusions: Risk factors for future laminitis prior to disease occurrence include low plasma adiponectin and high serum basal insulin or insulin post dexamethasone concentrations. This article is protected by copyright. All rights reserved.

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

Article

Mar 2016

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.

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

Article

Feb 2009
J EQUINE VET SCI

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.

The present state and future of laminitis research

Article

Nov 2012
EQUINE VET J

Apparent adiposity assessed by standardised scoring system and morphometric measurements in horses and ponies

Article

Feb 2009
VET J

This study described a scoring system for the assessment of apparent neck adiposity and evaluated morphometric measurements for assessment of neck and overall adiposity. Twenty-one barren Thoroughbred mares, 13 Arabian geldings and 75 Welsh, Dartmoor, or crossbred pony mares, were clinically examined and blood samples analysed for insulin, glucose, leptin, and triglycerides. Bodyweight (BW), height, length, girth and abdominal circumferences, neck length, neck crest height and neck circumference were measured, and body condition scores (BCS) and cresty neck scores (CNS) were rated.Girth:height ratio had the strongest associations with BCS (rs = 0.64, P < 0.001 in horses; rs = 0.83, P < 0.001 in ponies) and blood variables, such as leptin (rs = 0.39, P = 0.024 in horses; rs = 0.68, P < 0.001 in ponies). Crest height and neck circumference:height ratio had the strongest association with CNS (rs > 0.50, P < 0.01) and blood variables, such as insulin (rs ⩾ 0.40, P < 0.05).Cresty neck score was useful in the assessment of neck crest adiposity and had physiological relevance, as demonstrated by associations with blood variables. Girth:height was the most suitable morphometric for assessment of overall adiposity, and either crest height or neck circumference:height was a suitable morphometric for assessment of apparent neck adiposity.

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

Article

Aug 2011

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.

The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital

Article

Jun 2011

Endocrinopathic causes of laminitis may be a common underlying causative pathogenesis in first-opinion or field cases presenting with laminitis, as opposed to laminitis produced in inflammatory research models. This study aimed to determine whether evidence of an underlying endocrinopathy was present in horses presented for laminitis to a first-opinion/referral veterinary teaching hospital. A second aim was to compare the signalment of horses and ponies with laminitis with the equine hospital population during the same period. All horses presenting for laminitis at Helsinki University Equine Teaching Hospital, Finland, over a 16-month period were examined for an underlying endocrinopathy. Horses presenting for laminitis were compared with the hospitalized population over the same period. There were 36 horses presented for laminitis, and evidence of endocrinopathy was present in 89%. Of the horses showing an underlying endocrinopathy, one-third had a diagnosis of pituitary pars intermedia dysfunction, and two-thirds showed basal hyperinsulinemia indicative of insulin resistance, without evidence of hirsutism. Phenotypic indicators of obesity were present in 95% of horses with basal hyperinsulinemia without hirsutism. Compared with the hospital population during the same period, horses with laminitis associated with an underlying endocrinopathy were significantly older and more likely to be pony breeds. Our data support that endocrine testing should be performed on all cases of laminitis that do not have a clear inflammatory or gastrointestinal origin.

Equine laminitis: Induced by 48 h hyperinsulinaemia in Standardbred horses

Article

Mar 2010

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. 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. 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. 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. Healthy Standardbred horses subjected to prolonged hyperinsulinaemia develop laminitis within 48 h, demonstrating that laminitis in horses can be triggered by insulin. 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.

Prediction of incipient pasture-associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised and localised obesity in a cohort of ponies

Article

Feb 2009

The ability to predict ponies at increased risk of laminitic episodes, when exposed to nutrient dense pasture, would facilitate management to avoid disease. To identify variables and clinically useful cut-off values with reproducible diagnostic accuracy for the prediction of ponies that subsequently developed laminitis when exposed to nutrient dense pasture. A cohort of predominantly Welsh and Dartmoor ponies from a closed herd was evaluated in March 2006 (n = 74) and March 2007 (n = 57). Ponies were categorised as never laminitic or previously laminitic according to reported laminitic history and as clinically laminitic (CL) if laminitis was observed within 3 months following evaluation. Body condition score (BCS), cresty neck score (CNS), girth and neck circumferences (NC), withers height, blood pressure and hoof surface temperature, and plasma insulin, glucose, triglyceride, leptin, cortisol, ACTH, uric acid and TNF-alpha concentrations were measured. Analysis of sensitivity, specificity and receiver operating characteristic curves was used to evaluate the diagnostic accuracy for a variable to predict CL ponies. Variables with diagnostic accuracy for the prediction of CL ponies included insulin, leptin, BCS, CNS, and NC:height ratio. Specific cut-off values of insulin (>32 mu/l), leptin (>73 ng/ml), BCS (> or = 7), CNS (> or = 4) and NC:height ratio (>0.71) had reproducible diagnostic accuracy for the prediction of laminitis. Combining tests did not result in higher diagnostic accuracy than individual tests of insulin or leptin during either evaluation. Tests of insulin and leptin concentrations and measures of generalised (BCS) and localised (CNS or NC:height ratio) obesity were beneficial in the prediction of laminitic episodes. These results highlight the importance of monitoring and reducing insulin concentration, and generalised and regional obesity in ponies to reduce risk of laminitis.

Dietary Management of Obesity and Insulin Resistance: Countering Risk for Laminitis

Article

May 2009

Insulin resistance (IR) and hyperinsulinemia increase risk for development of laminitis in horses and ponies. Obesity also has been associated with heightened risk for laminitis, likely by means of development of IR. Dietary factors, particularly the nonstructural carbohydrate (NSC) load, modulate risk for laminitis in these animals by means of exacerbation of IR or gastrointestinal disturbances that trigger the condition. Specific dietary management strategies to lessen risk for laminitis include caloric restriction to promote weight loss and improve insulin sensitivity in obese animals and strict control of dietary NSCs, with elimination of grains and sweet feeds from the ration and restricted access to pastures that may be rich in NSCs. Medical treatment with levothyroxine or metformin may be indicated in animals that do not respond to conservative dietary management.

Relationship between condition score, physical measurements and body fat percentage in mares

Article

Nov 1983

Serum insulin concentrations in horses with equine Cushing's syndrome: Response to a cortisol inhibitor and prognostic value

Article

May 2004

Serum insulin concentration and its use as a prognostic indicator in horses with equine Cushing's syndrome (ECS) have been poorly documented. To examine daily insulin variations in horses with ECS and the effect of treatment using trilostane, a competitive inhibitor of 3beta-hydroxysteroid dehydrogenase. Further, we aimed to examine the relationship between baseline serum insulin concentration and survival in horses with ECS. Basal serum insulin concentrations were measured in 20 confirmed ECS cases by taking blood at regular 4 h intervals for 24 h (1200, 1600, 2000, 2400, 0400 and 0800 h) before treatment (Day 0) and 10 days, and 30 days and 1-2 years after the onset of trilostane therapy. The temporal pattern of insulin was analysed using a linear mixed model approach, and the prognostic value of measurements on Day 0 assessed using receiver-operating characteristic analysis. Horses with ECS showed a diurnal pattern of serum insulin concentration, highest value at 1200 h, and this pattern was not altered by treatment with trilostane. Furthermore, despite a mild increase of serum insulin concentrations after 10 days of trilostane therapy, insulin concentration was unaffected in the long-term. Low serum insulin concentrations at the beginning of the trial were significantly associated with improved survival to 1-2 years. The 1200 h sampling before treatment had the highest prognostic value for prediction of survival with a sensitivity and specificity of at least 90% for serum insulin at < 62 and > 188 microu/ml to predict survival and nonsurvival, respectively. Insulin is a useful prognostic indicator for ECS, but potentially large variations can occur throughout a 24 h period, indicating a single sample may not be representative. Serum insulin concentration did not increase over 1-2 years in horses receiving trilostane therapy.

Induction of laminitis by prolonged hyperinsulinaemia in normal ponies

Article

Dec 2007
VET J

The purpose of this study was to determine the effects of prolonged administration of insulin, whilst maintaining normal glucose concentrations, on hoof lamellar integrity in vivo on healthy ponies with no known history of laminitis or insulin resistance. Nine clinically healthy, unrelated ponies were randomly allocated to either a treatment group (n =5; 5.9+/-1.7 years) or control group (n =4; 7.0+/-2.8 years). The treatment group received insulin via a euglycaemic hyperinsulinaemic clamp technique modified and prolonged for up to 72 h. Control ponies were infused with an equivalent volume of 0.9% saline. Ponies were euthanized at the Obel grade 2 stage of clinical laminitis and hoof lamellar tissues were harvested and examined for histopathological evidence of laminitis. Basal serum insulin and blood glucose concentrations were 15.7+/-1.8 microU/mL and 5.2+/-0.1 mmol/L, respectively (mean+/-SE) and were not significantly different between groups. Mean serum insulin concentration in treatment ponies was 1036+/-55 microU/mL vs. 14.6 microU/mL in controls. All ponies in the treatment group developed clinical and histological laminitis (Obel grade 2) in all four feet within 72 h (55.4+/-5.5h), whereas none of the control ponies developed laminitis. There was no clinical evidence of gastrointestinal involvement and the ponies showed no signs of systemic illness throughout the experiment. The data show that laminitis can be induced in healthy young ponies, with no prior history of laminitis, by maintaining prolonged hyperinsulinaemia with euglycaemia. This suggests a role for insulin in the pathogenesis of laminitis, independent of hyperglycaemia, or alterations in hind-gut fermentation. For the clinician, early detection and control of hyperinsulinaemia may facilitate management of endocrinopathic laminitis.

The oral glucose test predicts laminitis risk in ponies fed a diet high in nonstructural carbohydrates

Abstract

No full-text available

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