​Bamford NJ, Potter SJ, Baskerville CL, Harris PA, Bailey SR
Influence of dietary restriction and low-intensity exercise on weight loss and insulin sensitivity in obese equids
Journal of Veterinary Internal Medicine December 2018 33(1) DOI: 10.1111/jvim.153​
​

See also:
Why Obese Horses Need Both Diet and Exercise - Christa Lesté-Lasserre, Apr 2019, www.thehorse.com

Pollard D, Wylie CE, Verheyen KLP, Newton JR
Identification of modifiable factors associated with owner-reported equine laminitis in Britain using a web-based cohort study approach
BMC Veterinary Research Feb 2019 15:59 https://doi.org/10.1186/s12917-019-1798-8

Eleanor Jones wrote in Horse & Hound April 2019 that "limiting grazing may increase laminitis risk", saying that horses that wore grazing muzzles for only part of the time they were at grass were more likely to develop laminitis than horses that wore a muzzle all of the time or not at all.

Also that horses that grazed for a brief period in the mornings were at greater risk of laminitis than those that went out all day, overnight or not at all.

Is this true?  Given that restricting grass has been one of the main management strategies to reduce the risk of laminitis, does the study really suggest what Jones reports?

The short answer is no - whilst the study has been written up to suggest some correlation between these factors, no causality is proven.

Danica Pollard's research asked owners to complete an online questionnaire to enter the study, and add updates during the study period.  The study lasted from August 2014 to December 2016, 2 years and 5 months including 3 seasonal rises.

Study figures:
1070 horses, but full data for only 978 horses - these 978 horses were equivalent to 974 Horse Years At Risk (HYAR).
of which 35.9% had a history of laminitis prior to the study - 384 out of 1070 horses.  Or up to 384 horses out of 978 with a history of laminitis prior to the study.
During the study period, 97 horses had laminitis, with 123 laminitis episodes reported, but there was full data for only 100 episodes.
75.3% of these 97 horses had a history of laminitis prior to the study - 73 out of 97 horses.
19 out of the 97 horses had more than 1 episode of laminitis during the study period.

​Muzzle use.
Owners were asked:
2.13 Are you currently using any methods to restrict grass intake? Please indicate all that apply.
 No
 Use a grazing muzzle
 Strip grazing
 Restricted turnout
 Other (please specify)

2.13.1 If your horse grazes with a grazing muzzle, please indicate if this is worn:
 All the time while gazing
​ Part of the time while grazing

Grazing muzzle use was recorded as 1 of 16 variables associated with active episodes of owner-reported laminitis.  There were 100 active episodes of owner-reported laminitis in a cohort of 978 horses and ponies, being 974 horse years at risk.
Laminitis episodes in a combined entry of horses wearing a grazing muzzle the whole time while grazing or not using a grazing muzzle at all was 89/100 out of 950 HYAR (~horses) that either wore a grazing muzzle the whole time while grazing or didn't use a grazing muzzle at all - so 9.37%.  The paper uses this as the hazard ratio reference.
Laminitis episodes in horses wearing a grazing muzzle part of the time while grazing was 11/100, out of 30 HYAR (~horses) that wore a grazing muzzle part of the time while grazing - so 36.7%.  The paper gives a hazard ratio of 3.6 to using a grazing muzzle part of the time while grazing compared to using a grazing muzzle the whole time while grazing combined with not using a grazing muzzle at all.

Ignoring the statistics (remember the quote: "There are three kinds of lies: lies, damned lies and statistics"!), 
the figures reported show that in 978 horses, there were 100 active episodes of laminitis, of which 89% had either been wearing a muzzle the whole time while grazing, or hadn't been wearing a muzzle at all, or presumably hadn't been grazing at all, and of which 11% had been wearing a muzzle part of the time while grazing.  

Grouping together horses that wore a muzzle the whole time while grazing or didn't use a muzzle at all  or didn't have any access to grass surely makes this comparison with horses that wore a muzzle some of the time pointless.  Presumably not all 978 horses had access to grass.  Why are horses with no access to grass at all having their incidence of laminitis compared with horses that grazed, with or without  a muzzle?

Putting aside the strange comparison groups, it is clear that incidence of laminitis was higher as a % of horses that wore a muzzle some of the time when grazing (36.7%) than incidence of laminitis as a % of horses that wore a muzzle all the time/didn't wear a muzzle/didn't graze (9.37%).  So why might this be?

1.  The risk of laminitis regardless of muzzle use was likely to be very different between the two groups (whole/no muzzle v part muzzle).  Although entry into the study with its weight tracker and body condition scoring help was biased towards owners of horses that tended to be overweight or suffer from laminitis (and the study was well publicized on laminitis-related support groups and social media pages), we are aware of several owners who entered horses that had never had any issues with laminitis or being overweight.  So some % of the 978 horses had no reason to be considered at greater than normal risk of laminitis, and therefore are unlikely to have ever worn a muzzle.  Owners generally don't muzzle their horses without good reason - or fear - so it's likely - and the authors will have this information - that the horses that wore a muzzle, either all the time or part of the time while grazing, had a history of laminitis, or were at least good doers and/or overweight, i.e. had a suspected if not actual increased risk of laminitis.  And therefore the 30 odd horses in the part muzzle group possibly all had a history of laminitis, or being overweight, i.e. had a higher risk of laminitis regardless of muzzle use, than some of the horses in the whole/no muzzle group.  

2.  Continuing the likelihood that horses in the part muzzled group had a history of laminitis, and knowing that  x-rays weren't submitted to prove that rotation from previous laminitis had been corrected and that they had adequate sole depth and concavity for comfort, perhaps increased movement associated with turnout  (compared to some horses with no turnout in the whole/no muzzle group) increased foot pain, but it wasn't new hormone-related laminitis that was seen. 

3.  Perhaps the owners of the part muzzled horses weren't so strict about low sugar/starch diets - after all, they were by implication allowing their horses to graze without a muzzle some of the time, compared to some of the horses in the other group being muzzled all the time. 

4.  However, perhaps the reason these horses were only muzzled part of the time was because, when they weren't muzzled, they were on very sparse grazing, or a track system, or grazing under trees where grass might be expected to contain less sugar, and perhaps this grazing was supplemented with hay, so owners felt muzzles should be removed to ensure sufficient intake of preserved forage.

5.  Or perhaps the reason these horses were only muzzled part of the time was because they spent some time in a herd situation where social behaviour was encouraged, e.g. mutual grooming, again perhaps on sparse grazing.  

Remember there were only 2 options and no box for supplementary information for this question - there could be a huge range of options between wearing a grazing muzzle all the time when grazing and wearing a grazing muzzle part of the time when grazing.

​Durham AE, Frank N, McGowan CM, Menzies-Gow NJ, Roelfsema E, Vervuert I, Feige K, Fey K
ECEIM consensus statement on equine metabolic syndrome
J Vet Intern Med. Published online 6 Feb 2019. doi: 10.1111/jvim.15423

MacLeod C
​Letter to the Editor regarding the ECEIM consensus statement on equine metabolic syndrome
J Vet Intern Med. Published online 18 April 2019 https://doi.org/10.1111/jvim.15501

​Durham AE, Frank N, McGowan CM, Menzies-Gow NJ, Roelfsema E, Vervuert I, Feige K, Fey K
Response to letter to the Editor regarding the ECEIM consensus statement on equine metabolic syndrome
J Vet Intern Med. Published online 16 April 2019 https://doi.org/10.1111/jvim.15503

The full paper is available:
Carmalt JL, Scansen BA
Development of two surgical approaches to the pituitary gland in the Horse
Vet Q. 2018 Dec;38(1):21-27. doi: 10.1080/01652176.2017.1415488 (PubMed)

Surgery for Equine Cushing’s Disease: A Possibility? KER Jan 2018

A major problem with this research is that the cause of PPID is not hyperplasia, hypertrophy or adenoma formation in the pituitary gland, it is loss of dopaminergic neurons in the hypothalamus.  Surgery on the pituitary gland will not reduce the primary cause of PPID.

Bear in mind that a lot of older research into PPID is based on untreated horses with advanced PPID - these horses may have had "grossly enlarged pituitary glands", but it is now being suggested that with earlier and better diagnosis of PPID, plus regular treatment with pergolide , either a constant low dose for several years (Schott H), or an initially higher dose that perhaps is reduced once symptoms are brought under control (Durham A), PPID may not progress to the advanced stage with hyperplasia and hypertrophy leading to adenoma formation.  

The paper suggests that daily treatment with oral pergolide is costly and "labor and management intensive".  Costly, yes, particularly when horses require higher doses of pergolide, and while the only licensed treatment for horses is Prascend.  However, the exclusive licence for Prascend expires in 2020 in the UK, and if other manufacturers enter the market, prices may come down.  "Labor and management intensive" - giving a daily pill to a horse, compared to serious, expensive and potentially life-threatening surgery?  Whilst it can be difficult to persuade some horses to take their daily medicine, how many owners would choose the latter - even if surgery was effective?  The authors suggest that giving daily pergolide to horses that are "extensively or pasture managed"  and "infrequently handled" may not be possible... frankly, such horses are probably fairly unlikely to have PPID diagnosed or to be treated for it if PPID were diagnosed.  Horses kept in these conditions are probably more likely to be young horses, and young horses don't get PPID.  The authors suggest that there is emotional stress for owners deailing with horses with a chronic ongoing disease.  But surgery to remove pituitary adenomas will not cure PPID (see below), and treatment with pergolide in many cases is extremely effective, allowing horses with PPID to live normal lives.  Are the authors identifying real problems?

Cushing's disease in dogs and humans is caused by a tumour in the pituitary gland. PPID in horses is caused by degeneration of dopamine-producing neurons in the hypothalamus (found in the lower part of the brain, above the pituitary gland), which, if not controlled through use of dopamine agonists like pergolide, can eventually lead to the formation of adenomas (benign tumours) in the pituitary gland. Prior to the formation of adenomas, an increase in the number and size of pars intermedia cells occurs because of the lack of stimulus to stop producing hormones - due to the reduced quantity of dopamine reaching the pituitary gland, the body is telling the pars intermedia to produce more hormones, and to do this, it has to increase its factory size...and eventually these increased cells form benign tumours called adenomas.

Removing these adenomas in cases of PPID will not stop the progression of PPID - it is the lack of dopamine that causes and drives the progression of PPID. There might be a short-term reduction in hormone output because the factory size has been reduced, but cells can often increase in number very quickly, so is it likely that cell numbers would quickly increase back to meet the hormone production the lack of dopamine is stimulating? Even if the surgery did help for a period of time, a horse would still need a treatment to replace the missing dopamine - so there is no way surgery could replace medical treatment. Well, not unless they could implant a slow-release dopamine replacement - that might be interesting.

The research was basically trying to find a surgical route to reach the pituitary gland in horses, which is perfectly reasonable.

The first attempts on cadavers were a myeloscopic approach which was abandoned due to too much bleeding, and a trans-sphenopalatine sinus approach that was abandoned due to inadequate access to the sinus, plus the proximity of the optic chiasm to the pituitary gland would make this technique unfeasible.  The pituitary gland was accessible with a ventral trans-basispheniodal osteotomy approach in cadaver heads, but when this was carried out on a live horse under anesthetic, a slip of the drill caused uncontrollable hemorrhage and the horse was euthanased.  An approach through the deep facial vein allowed access to the ventral cavernous sinus and the pituitary gland in cadaver heads.  This approach was then carried out on two live horses: access for a long flexible needle to the pituitary gland was achieved on one healthy horse, but on the other horse that had PPID, a needle injecting dye missed the pituitary gland and emptied into the cavernous sinus blood instead.  Both horses were euthanased while under the anesthetic, so recovery and adverse effects from this procedure are not known.  This procedure was technically demanding, with accurate positioning being critical, and possible additional complications including damage to blood vessels and nerves in the guttural pouch, with intractable dysphagia which can lead to pneumonia and death, and introduction of infection.  The authors note that this method would be likely to cause "collateral damage to the pars nervosa or pars distalis".

The authors state that it is not known how much surgical removal or cell destruction would be necessary to return a horse to being clinically normal, and that the goal would not be to remove all pars intermedia hormone output.  However, no mention is made of the fact that the pituitary abnormality is the result, not the cause, of PPID.  The authors state that "anything other that complete resolution of clinical signs will be unsuitable in the horse because there is already an oral daily medication for PPID" - but without daily medication to replace the dopamine not being produced by the hypothalamus, surely the cause of PPID will continue, and a horse could risk life threatening surgery for no great long-term improvement in clinical signs and continue to suffer from PPID.

The research is valuable for describing successful and unsuccessful approaches to the equine pituitary gland, but the article suggesting that this research "offers owners hope for viable alternatives to daily pergolide" is misleading.

​Jacob SI, Geor RJ, Weber PSD, Harris PA, McCue ME
Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses
Domest Anim Endocrinol. Published online 2017 Nov 1;63:15-22. doi: 10.1016/j.domaniend.2017.10.005

Abstract:Diagnosis of equine pituitary pars intermedia dysfunction (PPID) remains a challenge as multiple factors (stress, exercise, and time of year) influence ACTH and cortisol concentrations. To assess endocrine status in a study designed to evaluate the effects of age and diet on glucose and insulin dynamics, we performed thyrotropin-releasing hormone (TRH) stimulation tests and overnight dexamethasone suppression tests in March, May, August, and October on 16 healthy Thoroughbred and Standardbred mares and geldings. Horses were grouped by age: adult (mean ± SD; 8.8 ± 2.9 yr; n = 8) and aged (20.6 ± 2.1 yr; n = 8). None of the horses showed clinical signs (hypertrichosis, regional adiposity, skeletal muscle atrophy, lethargy) of pituitary pars intermedia dysfunction. Horses were randomly assigned to groups of 4, blocked for age, and fed grass hay plus 4 isocaloric concentrate diets (control, starch-rich, fiber-rich, and sugar-rich) using a balanced Latin square design. Data were analyzed using a multivariable linear mixed regression model. Baseline ACTH was significantly higher in aged horses (mean ± standard error of the mean; 60.0 ± 10.7 pg/mL) adapted to the starch-rich diet compared to adult horses (15.7 ± 12.0 pg/mL) on the same diet (P = 0.017). After controlling for age and diet, baseline ACTH concentrations were significantly increased in October (57.7 ± 7.1 pg/mL) compared to March (13.2 ± 7.1 pg/mL; P < 0.001), May (12.4 ± 7.1 pg/mL; P < 0.001), and August (24.2 ± 7.1 pg/mL; P < 0.001), whereas post-TRH ACTH was higher in August (376.6 ± 57.6 pg/mL) and October (370.9 ± 57.5 pg/mL) compared to March (101.9 ± 57.3 pg/mL; P < 0.001) and May (74.5 ± 57.1 pg/mL; P < 0.001). Aged horses had significantly higher post-dexamethasone cortisol on the starch-rich diet (0.6 ± 0.1 μg/dL) compared to the sugar-rich diet (0.2 ± 0.1 μg/dL; P = 0.021). Post-dexamethasone cortisol was significantly higher in October (0.6 ± 0.1 μg/dL) compared to March (0.3 ± 0.1 μg/dL; P = 0.005), May (0.2 ± 0.1 μg/dL; P < 0.001), and August (0.3 ± 0.1 μg/dL; P = 0.004). Breed did not influence ACTH or cortisol measurements. In conclusion, in addition to age and time of year, diet is a potential confounder as animals on a starch-rich diet may be incorrectly diagnosed with pituitary pars intermedia dysfunction.

Coleman M, Belknap J, Bramlage L, Eades S, Fraley B, Galantino-Homer H, Hunt R, Geor R, McCue M, McIlwraith W, Moore R, Peroni J, Townsend H, White N, Cummings K, Ivanek-Miojevic R, Cohen N
Case Control Study of Pasture and Endocrinopathy-Associated Laminitis in Horses
Equine Endocrinology Summit 2017 p 25

Significant efforts have been made in the past decade to further our understanding of laminitis in horses; however, much research has been limited to the study of the mechanistic pathways following experimental induction of disease. The conduct of observational studies of naturally-occurring laminitis is necessary for the improvement of our knowledge and understanding of disease predisposition and the design of future investigations into the prevention and control of this debilitating disease. Thus, the objective of this study was to determine risk factors for the development of pasture- and endocrinopathy-associated laminitis (PEAL) in horses evaluated by veterinarians in North America. In this case-control study, incident cases of PEAL evaluated by veterinary practitioners in North America from 2012- 2015 and horses from 2 control populations were included. Participating veterinarians provided historical data from a case of PEAL, a healthy control, and a lameness control. Conditional logistic regression analysis was used to compare data from PEAL-affected horses and each set of controls. A total of 199 horses with acute, incident PEAL, 198 healthy controls, and 153 lameness controls were included in the analysis.

Horses with an obese body condition (BCS ≥ 7), generalized or regional adiposity, a historic diagnosis of an endocrinopathy, and recent glucocorticoid administration were at increased odds of developing PEAL. 

Elucidating the determinants and earlier recognition of obesity, adiposity, and endocrinopathies might be a strategy for reducing the burden of this form of laminitis.

Update August 2018.  See also:
Coleman MC, Belknap JK, Eades SC, Galantino-Homer HL, Hunt RJ, Geor RJ, McCue ME, McIlwraith CW, Moore RM, Peroni JF, Townsend HG, White NA, Cummings KJ, Ivanek-Miojevic R, Cohen ND
Case-control study of risk factors for pasture-and endocrinopathy-associated laminitis in North American horses
J Am Vet Med Assoc. 2018 Aug 15;253(4):470-478. doi: 10.2460/javma.253.4.470

and The Laminitis Laboratory at New Bolton Center post 07 August 2018:
"Take-home bulletpoints from the study for risk factors for Pasture- and Endocrinopathy-Associated Laminitis (PEAL):
- Overweight body condition (BCS >/= 7 out of 9)
- Generalized or Regional adiposity (e.g., "cresty neck")
- Pre-existing endocrinopathy
- Not receiving concentrates in their diet (confounded by BCS since these horses/ponies were probably already recognized by owners/managers to be "easy keepers).
- Had received corticosteroids within 30 days (although presented with the caveat that the study included a low number of cases and controls that had received corticosteroids)
Tons of data collected by participating veterinarians all over the US and Canada made this study possible, which started as the group of authors meeting for a big brainstorming and study design session in Atlanta in 2010, many e-mail discussions, and a lot of hard work by Michelle Coleman of Texas A&M University, the lead author, and her thesis advisor during the study, Noah Cohen."

Let the laminitis data gathering begin! 
Ed Kane, dvm360, Apr 2012

Siciliano PD, Gill JC, Bowman MA
Effect of Sward Height on Pasture Nonstructural Carbohydrate Concentrations and Blood Glucose/Insulin Profiles in Grazing Horses
JEVS October 2017 vol 57, Pages 29–34

Highlights

• •Frequent mowing decreases pasture plant nonstructural carbohydrate concentration.
• •Horses grazing shorter sward height pasture have attenuated blood insulin response.
• •Maintaining shorter pasture sward height can potentially decrease laminitis risk.

AbstractSix mature stock-type geldings with maintenance only requirements were used in a randomized cross-over design to determine the effect of sward height on pasture plant nonstructural carbohydrate (NSC) concentrations and blood glucose and insulin concentrations. Horses were randomly assigned to one of two tall fescue (Lolium arundinaceum Schreb cv Max-Q, Pennington Seed, Madison, GA) grazing cells (0.37 ha) having two different sward heights for a period of 7 days: (1) short (approximately 15 cm; n = 3) or tall (between 30 and 40 cm; n = 3). After the first 7-day period, treatment groups were reversed by moving horses to ungrazed cells having similar characteristics to those used in the first 7 days, so that all horses receive all treatments resulting in six observations per treatment. Both short and tall grazing cells were mowed to a height of approximately 15 cm 32 days before the experiment starts. The short grazing cells were removed to approximately 15 cm at 11 days before the start of the first 7-day period and again 1 day before the start of each 7-day period. All horses had access to pasture for 10 h/d beginning at 8 AM and ending at 6 PM. Although not at pasture, all horses were individually housed in 3.7 × 12.2 m partially covered pens containing automatic water troughs and a crushed stone surface. Herbage mass (kg DM/ha) was determined by use of a falling plate meter for each pasture to ensure that both groups of horses had adequate dry matter to provide grazing for at least 7 days. On day 7 of each period, jugular venous blood samples were collected from each horse before being turned out to pasture, and then at 2, 4, 6, and 8 hours after turn-out. Pasture samples were also collected from each grazing cell at the same time blood samples were taken. Serum and plasma from blood samples were harvested and analyzed for insulin and glucose concentrations, respectively. Pasture samples were analyzed for water soluble carbohydrate (WSC), ethanol soluble carbohydrate (ESC), and starch. The sum of WSC and starch were used as an estimate of NSC. Area under the curve (AUC) and peak concentration were calculated for both plasma glucose (PPG) and serum insulin (PSI) concentration and were analyzed using analysis of variance for randomized cross-over designs. Pasture WSC, ESC, starch, and NSC concentrations were analyzed using analysis of variance for randomized complete block design. A P value of < .05 was considered significant. Mean pasture plant NSC, WSC, and ESC concentrations were lower (P < .001) in short as compared with tall. Pasture plant starch concentration was not different between treatments. Mean pregrazing plasma glucose concentrations, PPG concentrations, and plasma glucose AUC were not affected by treatment. Mean pregrazing serum insulin concentrations were not affected by treatment. Mean PSI and insulin AUC were greater (P < .01) when horses grazed tall, as compared with short. In conclusion, decreasing the sward height by mowing pasture decreased NSC, WSC, and ESC concentrations and subsequently decreased the postprandial insulin response of horses grazing the pasture. These findings may be important in developing strategies aimed at preventing insulin resistance in grazing horses.

See also

Regular pasture mowing has potential to reduce laminitis risk for horses, study finds - Horsetalk.co.nz July 2017

​Carslake HB, Pinchbeck GL, McGowan CM
Evaluation of a Chemiluminescent Immunoassay for Measurement of Equine Insulin
Journal of Veterinary Internal Medicine published online 26 January 2017

​Abstract
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.

Smith S, Harris PA, Menzies-Gow NJ
Comparison of the in-feed glucose test and the oral sugar test
Equine Veterinary Journal published online 7 MAY 2015 (PubMed)

Abstract
REASONS FOR PERFORMING STUDY:The in-feed oral glucose test (OGT) and oral sugar test (OST) are advocated as field tests of insulin sensitivity in horses and ponies but have not been directly compared.
OBJECTIVES:To compare the insulin response to OGT and OST in 8 ponies and 5 horses of unknown insulin sensitivity.
STUDY DESIGN:Experimental, randomised crossover study.
METHODS:Animals were fasted for 8 h overnight before and throughout testing. They were fed 1 g/kg bwt glucose powder with chaff (OGT) or 0.15 ml/kg bwt corn syrup (Karo™ Light Syrup; OST) was administered per os in a randomised crossover study with 48 h between tests. Blood samples were obtained at 0, 30, 60, 75, 90, 120 and 180 min. The maximal insulin concentration (Cmaxi ), time to maximal insulin concentration (Tmaxi ) and area under the curve of insulin concentration over time (AUCi ) for the tests were compared using Student's paired t test. The effect of individual subject, horse or pony and test were analysed using a linear mixed model.
RESULTS:The OGT Cmaxi (mean ± s.d.; 154 ± 116 μiu/ml), Tmaxi (136 ± 52 min) and AUCi (15,308 ± 9886 μiu/ml/min) were significantly (P<0.05) greater compared with the OST Cmaxi (72 ± 55 μiu/ml), Tmaxi (63 ± 25 min) and AUCi (5980 ± 4151 μiu/ml/min). The Cmaxi , Tmaxi and AUCi varied significantly between individual subjects. The Tmaxi was significantly different between horses and ponies during OGT and OST. Using previously defined criteria of insulin dysregulation, OGT identified 7/13 animals as insulin resistant, whereas OST identified 5/13 animals as insulin resistant.
CONCLUSIONS:The OGT and OST showed agreement in identification of insulin dysregulation in 85% of equine subjects. Results of the OGT and OST are not comparable in all cases. Further work is required to establish which test more accurately diagnoses insulin dysregulation in horses and ponies.