Predictors of laminitis development in a cohort of nonlaminitic ponies

Effects of pasture consumption and obesity on insulin dysregulation and adiponectin concentrations in UK native-breed ponies

BACKGROUND

Insulin dysregulation (ID) and hypoadiponectinaemia (total [adiponectin] <7.9 μg/mL) are risk factors for laminitis. They are sometimes, but not always, associated with obesity.

OBJECTIVES

To investigate the effects of pasture consumption and obesity on ID and circulating total [adiponectin] in ponies.

STUDY DESIGN

Longitudinal.

METHODS

Seven native-breed ponies with normal basal and post-oral sugar test (OST) [insulin] and body condition score (BCS) 4.3-5.5/9 were allowed to graze until they reached BCS 7/9. Ponies were then maintained at BCS 7/9 until completion of the study (week 22). Morphometric measures, OST, insulin tolerance test (ITT), plasma [adiponectin], whole-blood expression of receptors for adiponectin, insulin, and insulin-like growth factor 1, and pasture conditions (height and vigour) were determined fortnightly.

RESULTS

Median (range) BCS increased significantly (p < 0.001) from 5.0 (4.3-5.5; week 0) to 7.2 (5.7-7.5; week 22). Basal [insulin] did not change significantly over the study, but median post-OST [insulin] was significantly higher (p < 0.05) at week 14 (95.2 [17.9-114.0] μIU/mL), week 16 (103.0 [16.4-166.0] μIU/mL), and week 20 (93.6 [10.0-153.0] μIU/mL) than week 0 (25.0 [10.0-64.0] μIU/mL). Compared with week 0, ITT results were significantly lower at weeks 2-6 and 12-20, and [adiponectin] was significantly lower at weeks 10-22 (p < 0.05). [Adiponectin] decreased in all ponies during the study. Both low (3/10) and high (8-9/10) pasture scores were significantly associated with low ITT results. Low pasture scores were associated with low [adiponectin]. BCS was significantly associated with basal [insulin], post-OST [insulin], ITT results, but not [adiponectin].

MAIN LIMITATIONS

No control group with maintenance of ideal BCS; small sample size comprising native UK ponies.

CONCLUSIONS

Six ponies developed hypoadiponectinaemia, and all showed transient or consistent ID during the study. Both short, stressed grass and long, lush grass were associated with decreased tissue insulin sensitivity.

Evaluation of an Automated Fluorescence Enzyme Immunoassay for Quantification of Equine Insulin and Comparison to Five Other Immunoassays

BACKGROUND

Hyperinsulinemia is an important and treatable risk factor for laminitis in horses.

OBJECTIVES

Evaluate the Tosoh AIA-360 automated fluorescence enzyme immunoassay for the measurement of serum insulin concentrations in horses, and compare it to five other immunoassays for insulin quantification.

ANIMALS

One hundred serum samples from 83 horses were submitted for insulin measurement.

METHODS

The Tosoh AIA-360 was assessed against a reference assay (radioactive immunoassay; RIA). Using the same samples, TOS-FEIA, ELISA, and three chemiluminescent immunoassays (CLIA) were assessed for correlation and agreement with RIA.

RESULTS

The TOS-FEIA showed excellent correlation with RIA (r2 = 0.94, p < 0.0001) and good agreement, with a Bland-Altman constant bias (limits of agreement) of -23.8 μIU/mL (-74.6 to 27.0) and Passing-Bablok fit of y = -8.9 + 0.78x. Mean coefficients of variation were 1.8% for intra-assay and 5.7% for inter-assay precision, with mean recovery upon dilution of 104.2%. The assay comparison yielded good or excellent agreement (constant bias, limits of agreement) with RIA in the < 100 μIU/mL cohort for the ELISA (-7.0, -21.4 to 7.4) and the Cobas e CLIA (-31.4, -60.9 to -1.6). Spuriously high results (2 to > 10-fold of RIA result) were obtained in approximately 10% of results from both Immulite 2000 and 2000XPi CLIA analyzers, rendering the agreement poor.

CONCLUSIONS AND CLINICAL IMPORTANCE

The TOS-FEIA had acceptable accuracy and precision for clinical use, including at concentrations of insulin < 100 μIU/mL. The ELISA and one CLIA (Cobas e) showed acceptable accuracy, but the Cobas e demonstrated marked bias compared with RIA. Both Immulite CLIA assays exhibited unacceptable accuracy.

Horses with previous episodes of laminitis have altered insulin responses to seasonal oral sugar testing and grazing compared to horses with no known history of laminitis

Forage is essential for equine health and performance, but intake of elevated pasture nonstructural carbohydrates (NSC) may exacerbate metabolic disorders. This study aimed to investigate the influence of laminitis history on metabolic and morphometric responses in grazing horses. Twelve non-pregnant mares (15 ± 3.4 yrs) were selected based on previous diagnosis of laminitis (PRELAM; n=6) or not (NOLAM; n=6). Horses were maintained on 8.5-ha pasture. Weekly pasture samples were clipped at random for nutrient analysis. Monthly blood samples were collected and analyzed for glucose and insulin concentrations. Body weight (BW), body condition score (BCS), and cresty neck score (CNS) were evaluated monthly. Each month, a modified oral sugar test (OST) was used to assess basal (T0) and 75-minute (T75) insulin dynamics following 0.30 mL/kg BW Karo Light Corn Syrup. Data were analyzed using PROC MIXED with repeated measures (SAS Institute). PRELAM had greater CNS (P < 0.001), BW (P < 0.05), and BCS compared to NOLAM (P < 0.05). Non-fasted glucose was influenced by month (P < 0.001) while non-fasted insulin was affected by group by month (P = 0.004). Fasted insulin concentrations (T0) were affected by month and group (P < 0.001) where PRELAM had greater concentrations. T75 glucose and insulin concentrations were affected by month (P < 0.001 and P = 0.002, respectively) and were higher for PRELAM (P = 0.003). These data suggest horses with greater general and regional adiposity, and previous history of laminitis, often exhibit greater insulin concentrations on pasture and to OST.

Sodium-glucose transport protein 2 inhibitor use in the management of insulin dysregulation in ponies and horses

Laminitis is a common and painful condition of the equine foot and approximately 90% of cases are associated with insulin dysregulation (ID) that is a central feature of the common endocrine disorder equine metabolic syndrome (EMS) and occurs in a subset of animals with pituitary pars intermedia dysfunction. Additional features of EMS include obesity, altered circulating concentrations of adipokines (particularly adiponectin and leptin) and hypertriglyceridaemia. Obesity, ID, hypoadiponectinaemia, hyperleptinaemia and an altered plasma lipid profile are also features of human metabolic syndrome (HMS) alongside hyperglycaemia. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are a novel class of oral hypoglycaemic agents used in combination with lifestyle changes in the management of HMS. SGLT2 receptors are responsible for 90% of the renal glucose reabsorption that occurs in the proximal convoluted tubule. Thus, these drugs increase urinary glucose excretion by suppressing glucose reabsorption from the glomerular filtrate resulting in urinary calorie loss with consequent weight loss and improvements in ID, hyperglycemia, hypoadiponectinaemia and hyperleptinaemia. There are no licenced veterinary drugs available for treating ID and preventing insulin-associated laminitis in horses. Thus, the use of SGLT2i for the control of equine hyperinsulinaemia with the goal of improving recovery from associated active laminitis or preventing future laminitis has recently been advocated. There are a small number of published studies reporting the use of the SGLT2i canagliflozin, ertugliflozin and velagliflozin to aid the management of equine ID. However, the doses used are largely extrapolated from human studies with limited consideration of species-specific variations. In addition, there is limited evaluation of the fundamental differences between ID in horses and humans, particularly the fact that most horses with ID remain hyperinsulinaemic but normoglycaemic such that increased urinary loss of glucose may not explain the beneficial effects of these drugs. Further study of the potential deleterious effects of treatment-associated hypertriglyceridaemia is required together with the effect of SGLT2i therapy on circulating concentrations of adipokines in horses.

Short-term clinical and biochemical responses following treatment with dapagliflozin or ertugliflozin in horses with hyperinsulinemia: A retrospective case series

The metabolic and lipid profiles of horses treated with sodium-glucose cotransporter 2 inhibitors are not well understood. This retrospective study evaluated blood parameters in hyperinsulinemic horses treated with either ertugliflozin (0.05 mg/kg) or dapagliflozin (0.02 mg/kg) orally once daily. Blood samples were collected at baseline (day 0) and after 7 and/or 30 days of treatment. Statistical analyses were conducted using Wilcoxon signed-rank, Mann-Whitney and Spearman's rank correlation tests. Thirty-four horses received dapagliflozin and 24 received ertugliflozin. Significant (p<0.05) within-horse changes between day 0 and day 30 included [median, inter-quartile range (IQR)]: basal serum [Insulin] (uU/ml) reduced 170 (92-280) to 28.7 (14.5-90); [triglycerides] (mmol/l) increased 0.5 (0.3-0.6) to 1.0 (0.6-1.56), [β-hydroxybutyrate] (umol/l) increased 0.22 (0.17-2.7) to 0.30 (0.24-0.35); [total cholesterol] (mmol/l) increased 2.36 (2-2.6) to 2.84 (2.4-3.7); and GGT (IU/ml) increased 21 (16-32) to 25 (18-38). As a percentage of total serum lipids, high-density lipoprotein (HDL) reduced 52.4 % (47.9 %-61.0 %) to 50 % (41 %-54.8 %) and very-low density lipoprotein (VLDL) increased 10.4 % (6.4 %-14.4 %) to 12.3 % (9.9 %-16.8 %) (all p<0.05). Differences between ertugliflozin and dapagliflozin groups were not significant in any of these parameters at days 0, 7 or 30. At day 30, 10/48 (21 %) cases had [triglycerides] > 2.0 mmol/l (maximum = 10.8mmol/l). Day 30 [triglyceride] correlated with day 0: basal insulin (rho=0.47); [triglyceride] (rho=0.42); %VLDL (rho=0.34) day 30: [total cholesterol] (rho=0.67), %HDL (rho=-0.432) and %VLDL (rho=0.708). Our findings suggest that SGLT2 inhibitors induce minor changes in lipid profiles, with occasional cases of marked hypertriglyceridemia, and that dapagliflozin and ertugliflozin exhibit similar biochemical effects.

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

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.

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

In insulin dysregulation, hyperinsulinemia (HI) can be accompanied by peripheral insulin resistance (IR) in horses, which can be diagnosed with an insulin-tolerance test (ITT). The administration of 0.1 IU/kg body weight of recombinant regular human insulin (RHI) should elicit a 50 % reduction of the initial blood glucose concentration at 30 min after insulin administration in insulin sensitive horses. Compared to RHI, porcine zinc insulin (PZI) is veterinary-approved and therefore easier accessible for many practitioners. The aim of this study was to compare the insulin and glucose dynamics during a standard ITT with RHI to an ITT performed with PZI. Twelve Icelandic horses were subjected to an ITT with RHI (ITT-RHI) and with PZI (ITT-PZI) at same dosages in a randomised crossover design. The insulin and glucose dynamics that resulted from these tests were compared, and the consistency of classification into insulin-sensitive and IR categories was evaluated. No complications were observed with the use of either RHI or PZI in ITT. A good correlation of the test results was observed (r = 0.88; P < 0.001). The blood glucose concentrations and the percentage reduction in glucose concentration did not differ significantly between the two tests (P = 0.053), but four out of twelve horses were classified as IR in the ITT-RHI whereas with the ITT-PZI seven out of twelve horses were classified as IR with the 50 % glucose reduction from baseline. Based on the Youden index, when using the ITT-PZI, an adjusted cut-off value for blood glucose reduction of 40 % at 30 min resulted in better test performance. With consideration for the seemingly weaker effect of PZI and the adjusted cut-off value, PZI can be an appropriate substitute to RHI in an ITT.

Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis

Steroid-associated laminitis remains a major concern with use of corticosteroids in horses. Individual case factors such as joint pathology, pre-existing endocrinopathies, or corticosteroid type, dose, and timing influencing steroid-induced laminitis risk have not been investigated. This study aimed to determine if systemic absorption of triamcinolone acetonide (TA) varies between intrasynovial (antebrachiocarpal) and extrasynovial (sacroiliac) injection sites, and to determine the effects of TA absorption on glucose, insulin, cortisol, and adrenocorticotropic hormone (ACTH). Twenty adult horses were randomized into antebrachiocarpal or sacroiliac joint injection groups, and each horse received bilateral injections with a total dose of 18 mg triamcinolone. Blood was collected prior to injection and at 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 36, 48, 60, and 72 h post-injection. Peak TA absorption occurred at 8 h in both groups, and was significantly higher in the intrasynovial group compared to the extrasynovial group (1.397 ng/mL, 0.672 ng/mL, p < 0.05). Plasma TA levels were significantly higher in the intrasynovial group from 8 to 36 h post-injection (p < 0.05). There was no difference in glucose, insulin, cortisol, or ACTH between groups at any time point. Insulin and glucose were significantly increased from baseline at all timepoints from 10-72 h and 1-72 h post-injection, respectively. Horses with elevated baseline insulin values (>20 μU/mL) from both groups experienced a more marked hyperinsulinemia, reaching a mean peak insulin of 197.5 μU/mL as compared to 90.06 μU/mL in those with normal baseline insulin. Cortisol and ACTH were significantly decreased from baseline at timepoints from 4-72 h post-injection in both groups. This study is the first to evaluate drug absorption from the sacroiliac site and demonstrates that drug absorption varies between intrasynovial and extrasynovial injection sites. TA absorption causes metabolic derangements, most notably a marked hyperinsulinemia that is more severe in horses with elevated baseline insulin values. The influence of baseline endocrinopathies on response to corticosteroid administration as well as the effect of corticosteroid-induced metabolic derangements warrant further investigation as risk factors for corticosteroid-associated laminitis.

Insulin, but not adiponectin, is detectable in equine saliva using an automated, commercial assay

BACKGROUND

The hormones insulin and adiponectin are commonly measured in equids because of their involvement in endocrinopathic laminitis. These are currently measured in serum/plasma, although jugular venipuncture can cause stress in some animals and may be impossible in needle-shy individuals. However, both hormones can be measured in saliva in other species.

OBJECTIVES

To determine whether [insulin] and [total adiponectin] are detectable in equine saliva using automated assays and whether saliva collection is associated with changes in stress indicators. Additionally, the correlation between serum and salivary [insulin] was investigated.

STUDY DESIGN

In vivo experiment.

METHODS

Paired blood and saliva samples were collected from eight adult ponies at multiple time-points (n = 45 paired samples). [Insulin] and [total adiponectin] were measured using automated assays validated for equine serum/plasma. Blink rates and heart rates were determined, using video recordings and a wearable heart rate monitor respectively, to assess the effects of sample collection on stress indicators compared with a control situation without a stressful stimulus.

RESULTS

[Total adiponectin] was undetectable in saliva. However, salivary [insulin] was measurable with acceptable inter-assay (1.3 ± 0.9%) and intra-assay (1.1 ± 0.6%) variability. Blink and heart rates during saliva collection did not differ significantly from those in the control setting. Serum and salivary [insulin] were not significantly correlated.

MAIN LIMITATIONS

Small sample size comprising native UK ponies; potential sampling bias as animals were recruited to the study partly based on their behaviour during blood sampling; saliva collected from unfasted animals.

CONCLUSIONS

Insulin is measurable in equine saliva using an automated assay currently available in the UK, but further validation and the determination of specific diagnostic thresholds are required. Saliva collection was not associated with changes in stress indicators. Further research is therefore needed to determine the potential of equine saliva as a non-invasive alternative to blood for insulin determination.

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

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.

Short-term induced hyperinsulinaemia and dexamethasone challenge do not affect circulating total adiponectin concentrations in insulin-sensitive ponies

BACKGROUND

Hypoadiponectinaemia is a risk factor for endocrinopathic laminitis, but the directionality and nature of its association with insulin dysregulation is unclear.

OBJECTIVES

To investigate the effects of short-term induced hyperinsulinaemia and dexamethasone challenge on circulating [total adiponectin] and whole blood expression of adiponectin (AdipoR1 and AdipoR2), insulin, and insulin-like growth factor 1 (IGF-1) receptors in insulin-sensitive ponies.

STUDY DESIGN

In vivo experiment.

METHODS

Six never-laminitic, insulin-sensitive, native-breed UK ponies first underwent a dexamethasone challenge (0.08 mg/kg i.v.) with blood samples collected every 15 min over 3 h. After a 14-day washout period, hyperinsulinaemia was induced for 9 h via a euglycaemic-hyperinsulinaemic clamp (EHC), with blood samples collected every 30 min. Serum [insulin], plasma [total adiponectin], and plasma [IGF-1] were measured using validated assays and receptor gene expression was assessed via quantitative polymerase chain reaction (qPCR). Finally, whole blood was incubated with 10-1000 ng/mL dexamethasone for 3 h at 37°C to investigate its direct effects on gene expression.

RESULTS

There were no adverse effects observed during either protocol. Dexamethasone challenge did not alter circulating [insulin] or [total adiponectin] at any time-point, but significantly upregulated AdipoR1 and IGF-1R expression at 150 and 180 min. Ex vivo incubation of whole blood with dexamethasone did not alter expression of the genes examined. There was no change in [total adiponectin] or expression of the genes examined associated with EHC-induced hyperinsulinemia.

MAIN LIMITATIONS

This was a small sample size that included only native-breed ponies; total adiponectin was measured rather than high-molecular-weight adiponectin.

CONCLUSIONS

Short-term induced hyperinsulinaemia and dexamethasone challenge did not affect circulating [total adiponectin] in insulin-sensitive ponies. However, dexamethasone administration was associated with upregulation of two receptors linked to adiponectin signalling, suggesting that a physiological response occurred possibly to counteract dexamethasone-associated changes in tissue insulin sensitivity.

Development of a body condition index to estimate adiposity in ponies and horses from morphometric measurements

BACKGROUND

There is a high prevalence of obesity in ponies and pleasure horses. This may be associated with equine metabolic syndrome and an increased risk of laminitis. Body condition scoring (BCS) systems are widely used but are subjective and not very sensitive.

OBJECTIVES

To derive a body condition index (BCI), based on objective morphometric measurements, that correlates with % body fat.

STUDY DESIGN

Retrospective cohort study.

METHODS

Morphometric measurements were obtained from 21 ponies and horses in obese and moderate body condition. Percentage body fat was determined using the deuterium dilution method and the BCI was derived to give the optimal correlation with body fat, applying appropriate weightings. The index was then validated by assessing inter-observer variation and correlation with % body fat in a separate population of Welsh ponies; and finally, the correlation between BCI and BCS was evaluated in larger populations from studies undertaken in Australia, the United Kingdom and the United States.

RESULTS

The BCI correlated well with adiposity in the ponies and horses, giving a Pearson r value of 0.74 (P < 0.001); however, it was found to slightly overestimate the % body fat in leaner animals and underestimate in more obese animals. In field studies, the correlation between BCI and BCS varied particularly in Shetlands and miniature ponies, presumably due to differences in body shape.

MAIN LIMITATIONS

Further work may be required to adapt the BCI to a method that is more applicable for Shetlands and miniature ponies.

CONCLUSIONS

This BCI was able to provide an index of adiposity which compared favourably with condition scoring in terms of accuracy of estimating adiposity; and was more consistent and repeatable when used by inexperienced assessors. Therefore, this may be a useful tool for assessing adiposity; and may be more sensitive than condition scoring for tracking weight gain or weight loss in individual animals.

Factors associated with insulin responses to oral sugars in a mixed-breed cohort of ponies

BACKGROUND

Serum insulin concentration at 60 min (InsulinT60) during an oral sugar test (OST) indicates future laminitis risk and insulin dysregulation (ID). Associations between InsulinT60 and physical and owner-reported variables may help clinicians select individuals for ID testing. Associations between InsulinT60 and other metabolic markers may help elucidate ID pathophysiology.

OBJECTIVES

To describe associations between (A) season, physically-apparent and owner-reported factors and binary InsulinT60 interpretation (initial models) and (B) variables included in the initial models, other metabolic markers and continuous InsulinT60 (full models).

STUDY DESIGN

Prospective longitudinal.

METHODS

Non-laminitic ponies were examined and OSTs (0.3 mL/kg Karo syrup) performed every 6 months (autumn and spring) for ≤4 years. Factors associated with InsulinT60 were determined using mixed-effects models with physical, owner-reported, season and serum/plasma markers as fixed effects and pony and premises identifiers as random effects. Autumn and spring data were analysed separately for full models.

RESULTS

One thousand seven hundred and sixty-three OSTs from 367 ponies were included. High-risk InsulinT60 (>153 μIU/mL) was independently associated with (odds ratio, 95% confidence interval [CI]): age (1.36, 1.16-1.60), body condition score (BCS) (2.38, 1.21-4.69), and bulging supraorbital fatpads (7.25, 2.1-24.98). However, the initial models provided little explanatory power (Nakagawa R2  = 0.1-0.27). LoginsulinT60 was independently associated with (effect estimate, 95% CI): age (0.02, 0.01-0.04), Welsh/Welsh X breed (0.22, 0.05, 0.39), sex (gelding = -0.2, -0.34 to 0.06), BCS (0.16, 0.08-0.23), plasma adiponectin (-0.02, -0.02 to 0.01) and basal insulin (0.01, 0.01-0.01) in spring, and: age (0.03, 0.02-0.04), BCS (0.17, 0.08-0.26), bulging supraorbital fatpads (0.37, 0.2-0.54), turnout score (0.05, 0.02-0.09), plasma adiponectin (-0.01, -0.02 to 0.01), ACTH (per 10 pg/mL) (0.01, 0.00-0.01), triglycerides (0.28, 0.07-0.49) and InsulinT0 (0.01, 0.01-0.01) in autumn.

MAIN LIMITATIONS

Only non-laminitic ponies in one region were included.

CONCLUSIONS

Owner-reported and physically-apparent data were limited InsulinT60 predictors. InsulinT60 is a complex trait, independently associated with numerous variables, some with seasonal interactions.

Relationships between total adiponectin concentrations and obesity in native-breed ponies in England

BACKGROUND

Equine metabolic syndrome is a collection of risk factors associated with an increased risk of endocrinopathic laminitis. All affected animals display insulin dysregulation and some may show adiponectin dysregulation and/or excessive adiposity. However, the relationship between obesity and hypoadiponectinaemia in equids remains unclear.

OBJECTIVES

To investigate the relationship between obesity and circulating plasma total adiponectin (TA) concentrations in native-breed ponies in England.

STUDY DESIGN

Secondary data analysis.

METHODS

Data collected for three previous studies were retrospectively analysed and cohorts were pooled where possible (maximum sample size: n = 734 ponies). Correlations between [TA], age, and morphometric measures were assessed using Spearman's correlation coefficient. [TA] was compared between animals of different body condition score (BCS) classification (ideal-weight, overweight, and obese), breed, and body shape using Kruskal-Wallis with Dunn's post hoc tests, and sex using Mann-Whitney U test. The proportions of obese and ideal-weight ponies with basal hyperinsulinaemia and/or hypoadiponectinaemia were compared using a Chi-square test of homogeneity and post hoc z-test. Logistic regression was used to identify factors that may discriminate ponies with hypoadiponectinaemia.

RESULTS

[TA] was weakly positively correlated with BCS, height, weight, and weight:height ratio (Spearman's ρ = 0.14-0.29, p < 0.05). There were significant differences in [TA] in ponies with different BCS group classification, body shape, and breed. A greater percentage of obese (54.6%) than ideal-weight ponies (33.1%, p < 0.001) had both normal [TA] and [basal insulin], and a greater percentage of ideal-weight (38.6%) than obese ponies (16.5%, p < 0.001) showed hypoadiponectinaemia. Weight:height and BCS group were significant variables in a logistic regression of hypoadiponectinaemia but model fit and predictive accuracy were poor.

MAIN LIMITATIONS

Retrospective study design, only native-breed ponies included.

CONCLUSIONS

Morphometric measures such as BCS do not closely reflect [TA]. Circulating [TA] and [basal insulin] should be determined in all animals with predisposing factors, regardless of obesity status.

Epidemiological investigation of insulin dysregulation in Shetland and Welsh ponies in Australia

BACKGROUND

Insulin dysregulation (ID) is central to equine metabolic syndrome. There are limited epidemiological studies investigating dynamic testing of ID in ponies.

OBJECTIVES

To evaluate prevalence and risk factors for ID through dynamic testing of hyperinsulinaemia (DHI) and insulin resistance (IR).

STUDY DESIGN

Cross-sectional.

METHODS

Sex, age, breed, height, cresty neck score (CNS), body condition score (BCS), laminitis, HMGA2:c.83G>A genotype and pituitary pars intermedia dysfunction (PPID) status were documented. Dynamic hyperinsulinaemia was diagnosed with an oral sugar test (OST) and IR with an insulin tolerance test (ITT). Owners completed surveys reporting activity, laminitis history and perception of body condition using a (1-9) visual analogue scale (VASo). Ordinal scores were converted to binary outcomes for CNS (≤2/5 or ≥3/5), BCS and VASo (≤6/9 or ≥7/9). Variables associated with insulin concentrations, glucose reduction after the ITT and laminitis were evaluated with mixed effects regression models accounting for random effects of farms.

RESULTS

Among 167 ponies tested, median (range) age was 9 (4-21) years and BCS was 6 (4-8). Prevalence (95% confidence interval [CI]) of ID was 61 (53-68)%. Factors associated with insulin concentrations (estimate [95% CI]; μIU/mL) 60 min post-OST were: age (1.07 [1.02-1.11]), CNS (≥3/5, 1.52 [1.04-2.23]) and VASo (≥7/9, 1.75 [1.09-2.79]); and 90 min post-OST were: age (1.08 [1.03-1.12]), CNS (≥3/5, 1.80 [1.22-2.64]), VASo (≥7/9, 2.49 [1.52-4.08]) and sex (male, 0.64 [0.45-0.91]). Factors associated with glucose reduction after the ITT (estimate [95% CI]; %) were: age (-1.34 [-2.01 to -0.67]), sex (female, -6.21 [-11.68 to -0.74]) and VASo (≥7/9, -1.74 [-18.89 to -4.78]). Factors associated with laminitis (odds ratio [95% CI]) were DHI (4.60 [1.68-12.58]), IR (3.66 [1.26-10.61]) and PPID (11.75 [1.54-89.40]).

MAIN LIMITATIONS

Single time-point sampling, laminitis definition and diet analysis.

CONCLUSIONS

Ageing, being female and owner-perceived obesity were associated with ID.

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

Reference intervals (RIs) and clinical decision limits (CDLs) are frequently established to facilitate interpretation of values of endocrine biomarkers in the diagnosis of disease. Despite their commonplace use in clinical decision-making, these concepts can be confused. Comparing a test result with a RI provides an estimation as to whether or not the individual is healthy, whereas comparison with a CDL facilitates identification of individuals with a particular disease state or at greater risk of adverse clinical outcomes. In practice, there will also be a range of results for which the discriminative ability of the test is insufficient to inform a specific diagnostic decision. Including a range of uncertain test results, or 'grey zone', between positive and negative avoids the constraint of a binary decision in classifying an individual with a test value above (or below) a single cut-off value as diseased. This review will detail the application of both RIs and CDLs, including defining the range of uncertain test results, in the context of equine endocrinology.

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

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.

Prevalence and risk factors for laminitis within the Norwegian pony breed Nordlandshest/Lyngshest

BACKGROUND

Laminitis is a systemic condition resulting in debilitating pain and structural changes within the feet, and hence has major welfare implications. Causes include endocrine and systemic inflammatory conditions. Ponies are frequently affected, and observations in the field suggest that occurrence of laminitis is also common in Norwegian breeds. The aim of this study was to estimate the prevalence and risk factors for laminitis within the Norwegian pony breed Nordlandshest/Lyngshest.

RESULTS

The study was a cross-sectional study based on questionnaires sent to members of the Norwegian Nordlandshest/Lyngshest breed association. Questionnaires were received for 504 animals, of which 464 records were eligible and included in analyses. The population comprised 71 stallions, 156 geldings, and 237 mares, with an age between 1 and 40 years (median and interquartile ranges: 12 (6-18) years). The estimated 3-year period prevalence of laminitis was 8.4% (95% confidence interval (CI₉₅): 6.0-11.3%), whereas lifetime prevalence was 12.5% (CI₉₅: 9.6-15.9%). Mares had a significantly higher period- and lifetime prevalence of laminitis than male horses, and horses 10 years and older had a significantly higher prevalence than younger horses. The lifetime prevalence of laminitis was 3.2% in horses 9 years and younger, whereas from 17.3-20.5% in older horses. Multivariable logistic regression analysis identified age, sex, and regional adiposity as significantly (P < 0.05) associated with the 3-year period outcome of laminitis: Horses older than 9 years had a three-fold increase in the likelihood of having laminitis compared to the younger horses (Odds Ratio (OR)_10-14 years = 3.37 (CI₉₅ = 1.19-9.50), OR_15-19 years = 3.06 (CI₉₅ = 1.04-9.05), and OR_>20 years = 2.70 (CI₉₅ = 0.90-8.02). Mares were more than twice as likely (OR = 2.44 (CI₉₅ = 1.17-5.12) to have laminitis compared to male horses, and horses with regional adiposity had increased odds (OR = 2.35 (CI₉₅ = 1.15-4.82) of laminitis compared to horses without regional adiposity.

CONCLUSIONS

Laminitis appears to be a considerable welfare issue in the Norwegian pony breed Nordlandshest/Lyngshest. The identified risk factors age, sex, and regional adiposity highlight the need for improved owner education and awareness of strategies to reduce laminitis risk.

Equine Endocrine Disease: Challenges With Case Definition for Research

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.

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

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.

Effect of sirolimus on insulin dynamics in horses

BACKGROUND

Sirolimus, a mechanistic target of rapamycin inhibitor, suppresses insulin production in other species and has therapeutic potential for hyperinsulinemia in horses.

HYPOTHESIS/OBJECTIVE

Determine the pharmacokinetics (PKs) of sirolimus and evaluate its effect on insulin dynamics in healthy and insulin dysregulation (ID) horses.

ANIMALS

Eight Standardbred geldings.

METHODS

A PK study was performed followed by a placebo-controlled, randomized, crossover study. Blood sirolimus concentrations were measured by liquid chromatography-mass-spectrometry. PK indices were estimated by fitting a 2-compartment model using nonlinear least squares regression. An oral glucose test (OGT) was conducted before and 4, 24, 72, and 144 hours after administration of sirolimus or placebo. Effects of time, treatment and animal on blood glucose and insulin concentrations were analyzed using mixed-effects linear regression. Sirolimus was then administered to 4 horses with dexamethasone-induced ID and an OGT was performed at baseline, after ID induction and after 7 days of treatment.

RESULTS

Median (range) maximum sirolimus concentration was 277.0 (247.5-316.06) ng/mL at 5 (5-10) min and half-life was 3552 (3248-4767) min. Mean (range) oral bioavailability was 9.5 (6.8-12.4)%. Sirolimus had a significant effect on insulin concentration 24 hours after a single dose: median (interquartile range) insulin at 60 min (5.0 [3.7-7.0] μIU/mL) was 37 (-5 to 54)% less than placebo (8.7 [5.8-13.7] μIU/mL, P = .03); and at 120 min (10.2 [8.4-12.2] μIU/mL) was 28 (-15 to 53)% less than placebo (14.9 [8.4-24.8] μIU/mL, P = .02). There was minimal effect on glucose concentration. Insulin responses decreased toward baseline in ID horses after 7 days of treatment.

CONCLUSION AND CLINICAL IMPORTANCE

Sirolimus decreased the insulinemic response to glucose and warrants further investigation.