Pituitary Pars Intermedia Dysfunction Research Articles

Effect of short-term dopamine reduction on insulin sensitivity and post-prandial insulin and glucose responses in Standardbred horses

The role of dopamine in the regulation of insulin secretion in horses is poorly understood and requires further investigation. Pituitary pars intermedia dysfunction (PPID) is associated with decreased activity of dopaminergic neurons which normally suppress peptide hormone secretion from the pituitary pars intermedia. A high proportion of horses with PPID also have insulin dysregulation (ID), characterised by post-prandial hyperinsulinaemia and/or tissue insulin resistance, which are risk factors for the development of laminitis. The aim of this study was to investigate the effects of alpha-methyl-para-tyrosine (AMPT), a tyrosine hydroxylase inhibitor that reduces dopamine production, on insulin sensitivity and the post-prandial insulin response to a glucose-containing meal. Six healthy Standardbred horses were enrolled in a placebo-controlled randomised crossover study, in which one dose of AMPT (40 mg/kg BW) or placebo was administered orally, prior to performing an in-feed oral glucose test (OGT) and a frequently sampled intravenous glucose tolerance test (FSIGTT). Dopamine reduction by AMPT was confirmed by an increase in plasma prolactin concentration and the lack of post-prandial increase in plasma dopamine concentration compared to placebo. Post-prandial insulin responses, both peak and AUCi, were increased after AMPT compared to placebo (P=0.048 and P=0.005, respectively), without affecting blood glucose concentrations. However, one dose of AMPT did not appear to affect tissue sensitivity as assessed by the FSIGTT. This study confirmed that dopamine plays a role in the regulation of insulin secretion in horses, as it does in other species, whereby the post-prandial release of dopamine into the circulation may inhibit pancreatic insulin secretion. Further studies are required to evaluate different dosing protocols for AMPT, and to further investigate the links between PPID, ID and laminitis risk in horses.

Initial development of a rapid, portable, stall-side ELISA for the measurement of equine adrenocorticotropic hormone.

Pituitary pars intermedia dysfunction (PPID) is a neurodegenerative disease of senior horses. Loss of dopaminergic inhibition of the melanotropes of the pars intermedia leads to increased concentrations of pro-opiomelanocortin (POMC)-derived peptides. Diagnosis is challenging due to pre-analytical variables, such as sample storage, handling, and time to analysis. Our objective was to develop an ELISA for ACTH measurement, which could ultimately form the basis for a stall-side equine ACTH test. We selected 2 ACTH-specific monoclonal antibodies, CBL57 and EPR20361-248, based on the recognition of separate epitopes, strong and rapid color change, and minimal background interference, including no cross-reactivity with themselves, each other, and the test reagents. CBL57 was chosen as the detection antibody (or secondary antibody). EPR20361-248, functionalized on superparamagnetic iron oxide beads, was chosen as the capture antibody (or primary antibody) to bind ACTH in plasma. The incorporation of magnetic beads marks the initial stage in establishing a platform that could potentially be utilized in the field, similar to other stall-side tests. The concentrations of antibodies, magnetic beads, and incubation durations were optimized. Our immunoassay detected unglycosylated rat recombinant ACTH. Further studies are ongoing to optimize and validate our assay using equine plasma and serum samples.

Owner-reported health and disease in U.S. senior horses.

Information on health care and health status of U.S. senior horses (≥15 years of age) is currently sparse. (A) Provide an overview of owner-reported (1) medical conditions, (2) management/treatment practices for equine metabolic syndrome and pituitary pars intermedia dysfunction (PPID), (3) frequencies of routine health care practices and (4) supplement and pharmaceutical use in U.S. senior horses (≥15 years of age). (B) Evaluate potential risk factors for certain medical conditions and for low routine health care. Online survey. Descriptive and inferential analysis (binomial logistic regression and ANOVA) of 2717 questionnaires from owners of U.S. senior horses. The most common owner-reported veterinary-diagnosed medical conditions were osteoarthritis (30%), dental disorders (15%), lameness (14%), PPID (12%) and ocular disorders (6%). Advancing age was found to be a risk factor for PPID (odds ratio [OR] [95% confidence interval, CI] = 1.14 [1.10-1.18]), dental (OR [95% CI] = 1.18 [1.15-1.22]) and ocular (OR [95% CI] = 1.05 [1.01-1.10]) disorders. Only 36% of horses were free of owner-reported veterinary-diagnosed medical conditions at the time of the survey. During the year prior to the survey, most routine healthcare practices (i.e., veterinary health care, dental care and anthelmintic treatment) were typically undertaken one to two times per year, while farrier visits occurred mostly every 5-6 weeks. Retired senior horses had a higher risk of no health care visits (OR [95% CI] = 2.1 [1.38-3.06]), no dental care (OR [95% CI] = 2.0 [1.31-3.00]) and low farrier attendance (i.e., ≤4 times/year) (OR [95% CI] = 2.4 [1.57-3.63]) compared with senior horses used for pleasure riding. The most frequently administered drug was firocoxib (18%) and joint supplements were the most provided supplements (41%). Potential recall, response and sampling bias. Risk factor analyses do not establish causal relationships. Medical conditions are highly prevalent in U.S. senior horses. Retired senior horses have an increased risk of low routine health care.

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.

The detection of ACTH and insulin in equine plasma by solid-phase extraction and micro-flow LC/MSMS.

Previous liquid chromatography/mass spectrometry (LC/MS) methods for the detection of insulin and other similar peptide hormones in equine plasma relied on the use of antibody affinity extraction. As a result, these methods were not suitable for routine high-throughput analysis. A solid-phase extraction (SPE) method incorporating size exclusion as well as reversed-phase interactions allows the selective extraction of peptide hormones such as adrenocorticotropic hormone (ACTH), insulin and their synthetic analogues from equine plasma with approximately 80% extraction efficiencies. This extraction was combined with on-column derivatisation with acetic anhydride, followed by tryptic digestion and analysis by micro-LC/MSMS for high-sensitivity peptide hormone detection. The analysis of tryptic peptides provides greater sensitivity and more robust chromatography compared with the analysis of intact insulin and ACTH. For quantitative analysis, isotopically labelled internal standards of target peptides can be prepared in the laboratory through the use of deuterated acetic anhydride. The utility of the method was assessed for the analysis of ACTH and insulin in samples from horses suffering from pituitary pars intermedia dysfunction (PPID).

Strongyle egg shedding and egg reappearance periods in horses with pituitary pars intermedia dysfunction

Pituitary pars intermedia dysfunction (PPID) is the most common endocrine disorder of older horses. Immune dysfunction in horses with PPID could increase susceptibility to infectious diseases, including strongyle infections; however, few data are available. The aim of this study was to determine if horses with PPID had increased strongyle faecal egg counts (FEC) compared with control horses, over a fourteen-week period in Victoria, Australia. Clinical signs and plasma adrenocorticotropic hormone (ACTH) concentrations were used to categorise horses into PPID (n=14) or control (n=31) groups. Faecal samples were collected for FEC determination prior to anthelmintic treatment, and fortnightly post-treatment for each horse. Generalised linear mixed modelling, using a gamma distribution, was used to compare differences between groups in the repeated measures study. The confounding variable of age was controlled for as a fixed effect. Following anthelmintic treatment, mean FEC was greater for the PPID group compared to the control group on day 56 (405 ± 756 eggs per gram [EPG] vs 40 ± 85 EPG, p=0.05) and day 70 (753 ±1598 EPG vs 82 ±141 EPG, p=0.04). There were no differences in mean FEC between groups on days 84 and 98. Cumulative FEC (day 14 to day 98) was significantly greater for the PPID horses than control horses (2118 ± 4016 EPG vs 798 ± 768 EPG, p<0.0001). Group egg reappearance period was shorter for PPID horses (day 56 post-anthelmintic treatment) compared to control horses (day 70) and 30% of the PPID horses reached a FEC threshold of >200 EPG on day 42, compared to 0% of control horses (p=0.02). These results suggest that the rate of a re-established patent infection between groups could be different due to a comprised immune response in PPID horses or differences in the host-parasite relationship regarding encysted stage larvae. However, despite differences between groups, some horses with PPID consistently had no detectable or low FEC (<200 EPG) during the study period. These findings highlight the importance of individual FEC monitoring to determine if anthelmintic treatment is required, in line with sustainable parasite management practices.

Metabolic and Endocrine Insights in Donkeys.

Donkey medicine is gaining attention due to their increased use as companion animals, in shows, asinotherapy, etc. The increasing demand and unique aspects call for specialized care, requiring new information (physiology, infectious disorders, pharmacology, etc.). Since obesity is common in this species, hyperlipemia, metabolic syndrome and insulin dysregulation (ID) are common disorders in donkeys, in some cases with high mortality, either directly (multiorgan dysfunction) or indirectly due to poor quality of life (chronic laminitis). Donkeys have long-life expectancy and are often afflicted with pituitary pars intermedia dysfunction (PPID), a neurodegenerative and endocrine disease. Hyperlipemia is diagnosed based on high plasma triglyceride concentration in association with clinical findings and laboratory abnormalities from affected tissues (liver, kidney and pancreas). The measurement of resting serum insulin and plasma ACTH concentrations is the first step in ID and PPID diagnosis. In donkeys with clinical signs of ID (obesity or recurrent laminitis) or PPID (hypertrichosis, regional adiposity, laminitis and weight loss), where these hormones are in the normal or non-diagnostic range (donkey-specific cut-off values and reference ranges need to be established), dynamic tests are recommended (oral sugar test or thyrotropin-releasing hormone, respectively). Equine treatment protocols apply to donkeys, although pharmacological studies for most drugs, except pergolide, are lacking.

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

Insulin dysregulation (ID) is central to equine metabolic syndrome. There are limited epidemiological studies investigating dynamic testing of ID in ponies. To evaluate prevalence and risk factors for ID through dynamic testing of hyperinsulinaemia (DHI) and insulin resistance (IR). Cross-sectional. 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. 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]). Single time-point sampling, laminitis definition and diet analysis. Ageing, being female and owner-perceived obesity were associated with ID.

Lumbar vertebral bone density is decreased in horses with pituitary pars intermedia dysfunction.

Pathological fractures have been reported in equids with pituitary pars intermedia dysfunction (PPID) but their prevalence and pathogenesis is unknown. To compare: (1) bone mineral density (BMD) in weight bearing and nonweight bearing bones in PPID+ equids and aged and young PPID- controls; and (2) biomechanical properties of the fourth lumbar vertebral body in PPID+ equids and aged PPID- equids. Case-control study: five PPID+ equids and six aged and four young PPID- control horses. PPID status was based on clinical signs and necropsy examination of the pituitary gland (PG). The lumbar vertebral column, right front third metacarpus (MC3), left hind third metatarsus (MT3), and PG were removed after euthanasia. BMD was determined by quantitative computed tomography of regions of interest (ROI) in each bone and biomechanical testing was performed on the fourth lumbar vertebral body. Serum concentrations of parathormone (PTH), ionised Ca++ , 25-hydroxyvitamin D, and osteocalcin (OC) were also measured. Data were analysed using one-way ANOVA and correlation analyses. BMD of trabecular and cortical regions of interest (ROI) of the third, fourth (L4), and fifth lumbar vertebrae were significantly lower in PPID+ equids as compared with aged (p < 0. 001) and young (p < 0.01) PPID- controls. In contrast, no differences were found in BMD of trabecular or cortical ROIs of MC3 and MT3 between groups. No differences were detected in force at fracture, displacement at fracture, Young's modulus or strain of L4 between PPID+ and aged PPID- horses. No differences were found in serum PTH, ionised Ca++ , 25-hydroxyvitamin D, or OC concentrations between groups. Limited number of equids studied and variation in test results. BMD of nonweight bearing bones can be decreased with PPID and could increase risk of developing pathological fractures.

Influence of feeding and other factors on adrenocorticotropin concentration and thyrotropin-releasing hormone stimulation test in horses and ponies.

The basal (bACTH) and post-thyrotropin-releasing hormone stimulation concentration of adrenocorticotropin (pACTH) are recommended for diagnosis of pituitary pars intermedia dysfunction (PPID). Many factors influence bACTH (e.g., disease, age, month) and some affect the results only in autumn (e.g., breed, colour, sex). There are discrepancies about the impact of feeding on b/pACTH. To determine whether feeding, month, age, breed, colour, sex and body condition score affect b/pACTH. Prospective crossover. Sixty-one animals were divided into groups: healthy, PPID, treated-PPID. The b/pACTH was measured three times (1 mg protirelin; blood collection after 10 min; mid-November to mid-July) after different feedings: fasting, hay, hay + grain. Friedman's test was applied to evaluate the influence of feeding on b/pACTH and linear mixed model to evaluate impact of further factors. The b/pACTH was not significantly affected by feeding (p = 0.7/0.5). The bACTH was lowest in healthy (29.3 pg/mL, CI 9-49.5 pg/mL) and highest in PPID-group (58.9 pg/mL, CI 39.7-78.1 pg/mL). The pACTH was significantly lower in healthy (396.7 pg/mL, CI 283.2-510.1 pg/mL) compared to PPID (588.4 pg/mL, CI 480.7-696.2 pg/mL) and treated-PPID group (683.1 pg/mL, CI 585.9-780.4 pg/mL), highest in July (881.2 pg/mL, CI 626.3-1136.3 pg/mL) and higher in grey (723.5 pg/mL, CI 577.5-869.4 pg/mL) than other colours (338.7 pg/mL, CI 324.8-452.5 pg/mL). The size of effect for those variables was >0.5. Small number of animals, subsequent bACTH measurements were significantly lower in each horse. There was no evidence that feeding influences the b/pACTH. There was evidence that pergolide affects the bACTH but it had little effect on pACTH. Further investigation of the impact of month and coat colour on b/pACTH is warranted to better interpret the results.

Insulin signaling in insulin-dysregulated Icelandic horses

The underlying molecular mechanisms leading to insulin dysregulation are poorly understood in horses. Therefore, this study aimed to determine if insulin dysregulation is associated with an altered basal expression and extent of phosphorylation of key proteins of the insulin signaling cascade in liver (LT), muscle (MT), and subcutaneous adipose tissue (AT) under basal and stimulated conditions. Twelve Icelandic horses were subjected (1) to an oral glucose (Gluc PO) challenge and (2) to an intravenous (Ins IV) insulin challenge in a crossover study. Biopsies of LT, MT, and AT were taken in vivo under basal conditions and after Gluc PO and Ins IV stimulation. Corresponding insulin levels were measured by an equine optimized ELISA (Mercodia AB, Uppsala). Insulin levels ≥ 110 µIU/mL at 120 min indicated that six horses were insulin dysregulated (HI), while six were not (NI). Gluc PO stimulation resulted in a more pronounced hyperinsulinemia and hyperglycemia in HI horses compared to NI horses. Western blot analysis of key proteins of the insulin signaling cascade revealed an enhanced phosphorylation of the insulin receptor (InsR) under Gluc PO (P = 0.001) and Ins IV stimulation (P = 0.017) within LT, but not in MT and AT. Phosphorylation of protein kinase B was enhanced under Gluc PO stimulation in all tissues and under Ins IV stimulation in MT and AT, while phosphorylation of adenosine monophosphate protein kinase α was reduced after glucose administration (P = 0.005) in all horses. Interestingly, HI horses had significantly higher amounts of phosphorylated mechanistic target of rapamycin (mTOR) in MT (P = 0.049), irrespective of any stimulation. In LT, the amount of phosphorylated mTOR decreased under Gluc PO conditions in HI horses, while an increase was observed in NI horses (P = 0.015). A major limitation was the inclusion of only Icelandic horses of advanced age since insulin dysregulation could be related to both the equine metabolic syndrome and/or pituitary pars intermedia dysfunction. In summary, insulin signaling appeared to be maintained in both HI and NI Icelandic horses, although post-receptor alterations were observed. Thus, ID might be an equine-specific metabolic condition, in which alterations of the mTOR signaling pathway may play a crucial role, as emphasized by higher mTOR phosphorylation in HI horses.

Evaluation of seasonal influences on adrenocorticotropic hormone response to the thyrotropin-releasing hormone stimulation test and its accuracy for diagnosis of pituitary pars intermedia dysfunction

Pituitary pars intermedia dysfunction (PPID) is an age-related neurodegenerative disorder, affecting >20 % of older horses. There is a need for improved endocrine tests for early disease detection, and the thyrotropin-releasing hormone (TRH) stimulation test has been recommended for diagnosis of early or mild cases. However, it is currently not recommended for year-round use due to marked seasonal variability. The aims of this cohort study were to evaluate effects of month and season on adrenocorticotropic hormone (ACTH) responses to TRH stimulation and to derive monthly cut-offs for PPID diagnosis.Sixty-three horses were assigned to control (n = 17), subclinical PPID (n = 21) and clinical PPID (n = 25) groups, based on a composite reference standard that combined clinical history and examination findings with endocrine test results. TRH stimulation tests were performed monthly for a 12-month period. Circannual changes were evaluated with one- and two-way repeated-measures analysis of variance and receiver operating characteristic curve analysis was used to derive cut-off values for basal and TRH-stimulated ACTH. TRH-stimulated ACTH concentrations were lowest in February-May and highest in August-October. Specificity of both basal and 30 min post-TRH ACTH was generally higher than sensitivity, and TRH stimulation had improved diagnostic accuracy compared to basal ACTH, although its sensitivity was not significantly greater year-round. TRH stimulation tests yielded considerably more positive results than basal ACTH in the subclinical group, but few additional positive results in clinical PPID cases. There were large differences between cut-offs that maximised sensitivity or specificity for TRH-stimulated ACTH, highlighting the importance of considering clinical presentation alongside test results in diagnostic decision-making.

Diagnosis of equine pituitary pars intermedia dysfunction

Equine pituitary pars intermedia dysfunction (PPID) is common in aged horses. The majority of horses respond well to treatment, but treatment is lifelong, meaning accurate diagnosis of PPID is important. Similar to any condition, there is no perfect laboratory test to diagnose PPID and accuracy is affected by the characteristics of the population in which the test is being evaluated. This review details the importance of consideration of clinical factors and diagnostic test accuracy. Basal adrenocorticotrophic hormone (ACTH) concentration is used most frequently in practice and has very good diagnostic accuracy when used in combination with clinical judgement and the correct application of diagnostic thresholds. The thyrotropin-releasing hormone stimulation test can be used in horses with equivocal test results following basal ACTH testing, or to evaluate subtle cases due to its improved accuracy.

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

Blood glucose concentration is often measured during an oral glucose test (OGT), but is not thought to aid in diagnosing insulin dysregulation (ID) or pituitary pars intermedia dysfunction (PPID). The aim of this retrospective study was to investigate whether the change in blood glucose concentration during an OGT aligned with indicators of equine metabolic syndrome or PPID, including serum insulin and plasma ACTH concentrations, clinical observations, age, sex, breed type and the test dose. The cohort included 149 horses, miniature horses, and ponies that had undergone an in-feed OGT and clinical examination between 2015 and 2021. The animals were diagnosed as either metabolically healthy, insulin-dysregulated, having PPID or both endocrinopathies. The mean ± standard error increase in blood glucose during the OGT was 3.41 ± 0.21 mM, and this change showed a weak positive correlation with the increase in serum insulin concentration (r = 0.36; P 0.001), body condition score (BCS; r = 0.26; P = 0.002) and cresty neck score (CNS; r = 0.38; P 0.001). The median [interquartile range] increase in blood glucose for miniature horses (5.25 [2.98–6.5] mM), was more than twice that seen in full-sized horses (2.4 [1.33–3.45] mM; P = 0.03). In metabolically healthy animals the increase in blood glucose during an OGT (+2.2 [1–3.5] mM) was smaller (P 0.001) than in animals with ID (+3.8 [2.73–5.33] mM), or both endocrine diseases (+6.1 [3.6–6.85] mM). There was an effect of the dose of dextrose on the blood glucose response, with higher doses yielding larger responses (P 0.001). The variability in these data support that basal and post-prandial blood glucose responses to an OGT are not appropriate as stand-alone diagnostic markers of ID or PPID. However, the association between blood glucose and CNS supports the use of CNS when evaluating animals for ID.

Clinical implications of imprecise sampling time for 10- and 30-min thyrotropin-releasing hormone stimulation tests in horses.

The thyrotropin-releasing hormone (TRH) stimulation test is used to diagnose pituitary pars intermedia dysfunction (PPID) using 10- or 30-min protocols. Imprecise sampling time for the 10-min protocol can lead to misdiagnoses. To determine the effect of imprecise sampling time for the 30-min protocol of the TRH stimulation test. In vivo experiment. Plasma immunoreactive adrenocorticotropin (ACTH) concentrations were measured 9, 10, 11, 29, 30 and 31 min after intravenous administration of 1 mg of TRH in 15 control and 12 PPID horses. Differences in ACTH concentrations between sampling times, variability in ACTH concentrations between protocols, and diagnostic classification of PPID were assessed using Friedman's test, Bland-Altman plots, and Fisher's exact test, respectively, with 95% confidence intervals reported and significance set at p < 0.05. Imprecise sampling time resulted in variable ACTH concentrations, but significant differences in absolute ACTH concentrations were not detected for imprecise sampling within each protocol or between protocols. Imprecise sampling changed PPID diagnostic classification for 3/27 (11 [4-28] %) horses for both protocols. Using the 30-min protocol as a reference, 1/12 (8 [1-35] %) horses returned a negative test result and 5/12 (42 [19-68] %) horses returned equivocal test results that would be considered positive in practice due to the presence of supportive clinical signs. Limited sample size and inter-horse variability reduced the ability to detect small but potentially relevant differences. Overall, the impact of imprecise sampling was not significantly different between the 10- and 30-min TRH stimulation test protocols. However, diagnostic classification for PPID would have varied between the 10- and 30-min protocols in this population, if clinical signs had been ignored. Precise timing during TRH stimulation tests and contextual interpretation of ACTH concentrations remain fundamental for the diagnosis of PPID.

Retirement risk factors, exercise management and muscle mass in US senior horses.

Information on the management and health of US senior horses (≥15 years of age) is currently limited. Provide information on (1) primary use of US senior horses, (2) reasons and risk factors for horse retirement, (3) exercise management, (4) prevalence of low muscle mass and (5) risk factors for, and owner-perceived consequences of, low muscle mass. Online survey. Survey responses from 2717 owners of U.S.-resident senior horses (≥15 years of age) were analysed descriptively and inferentially, using ordered and binomial logistic regression, ANOVA and the Kruskal-Wallis test. The most frequently reported primary uses were pleasure riding/driving (38.5%) and full retirement (39.8%). Most horses (61.5%) were retired between 15 and 24 years of age, with health problems being the main reason. Age, female sex, Thoroughbred breed and various medical conditions were identified as risk factors for retirement. In working horses (i.e., those not retired or semi-retired), exercise intensity was negatively associated with age. The owner-reported prevalence of low muscle mass in all horses was 17.2% (95%CI = 15.7-18.7). In those affected by low muscle mass, the ability to work and welfare-related aspects were commonly perceived to be impaired. Increasing age, sex (gelding), pituitary pars intermedia dysfunction, osteoarthritis, laminitis and primary use (retired and semi-retired vs. use for competition) were identified as risk factors for owner-reported low muscle mass. Potential response, recall and sampling bias. Causal relationships cannot be established. Although structured exercise into old age may provide health benefits (as seen in elderly people), a large proportion of horses were fully retired in the current study. Senior horses were mainly retired for health problems and characterising these problems may aid in extending their work/active life. Low muscle mass was perceived to affect horses' welfare and ability to work, and identification of prevention and treatment strategies is therefore warranted.

Definition, Assessment, Health Consequences and Management of Equine Obesity: A Review

Abstract Obesity is a state of abnormal or excessive fat accumulation. Obesity in horses increases the risk of developing a variety of health issues such as: insulin dysregulation (ID), reduced athleticism, colic, abnormal reproductive performance, laminitis, endotoxaemia, diabetes mellitus, hyperlipaemia, impaired thermoregulation, pituitary pars intermedia dysfunction, and osteochondrosis. Obesity is a significant health and welfare issue in horses that may go unreported or unnoticed due to a caregiver’s (owner) neglect. Weight gain occurs when a horse’s energy consumption exceeds his or her physical energy needs. Obesity is best assessed via necropsy or upon in vivo assessment with deuterium oxide administration, although this is not feasible in a clinical environment. In practice, obesity is assessed by: body condition scoring, cresty neck scoring, ultrasono graphic assessment, morphometric measurements, or biochemical indicators in the blood. Dietary and exercise programs are the primary means of controlling equine obesity. Pharmacologic assistance (levothyroxine sodium and metformin hydrochloride), being a secondary approach, may be effective in some cases. Management involves a long-term plan that requires the horse’s caregiver’s effort and discipline, as well as the support and supervision of their veterinarian. This paper outlines the assessment, health consequences, and management of equine obesity.

Investigation of breed differences in plasma adrenocorticotropic hormone concentrations among healthy horses and ponies

Plasma adrenocorticotropic hormone (ACTH) concentration is commonly measured to diagnose pituitary pars intermedia dysfunction (PPID). Several intrinsic and extrinsic factors affect ACTH concentrations, including breed. The objective of this study was to prospectively compare plasma ACTH concentrations among different breeds of mature horses and ponies. Three breed groups comprised Thoroughbred horses (n = 127), Shetland ponies (n = 131) and ponies of non-Shetland breeds (n = 141). Enrolled animals did not show any signs of illness, lameness or clinical signs consistent with PPID. Blood samples were collected 6 months apart, around the autumn equinox and spring equinox, and plasma concentrations of ACTH were measured by chemiluminescent immunoassay. Pairwise breed comparisons within each season were performed on log transformed data using the Tukey test. Estimated mean differences in ACTH concentrations were expressed as fold difference with 95 % confidence intervals (CI). Reference intervals for each breed group per season were calculated using non-parametric methods.In autumn, higher ACTH concentrations were found among non-Shetland pony breeds compared with Thoroughbreds (1.55 fold higher; 95 % CI, 1.35–1.77; P < 0.001), and in Shetland ponies compared with Thoroughbreds (2.67 fold higher; 95 % CI, 2.33–3.08; P < 0.001) and non-Shetland pony breeds (1.73 fold higher; 95 % CI, 1.51–1.98; P < 0.001). In spring, no differences were identified among breed groups (all P > 0.05). Reference intervals were similar among breed groups in spring, but upper limits for ACTH concentrations were markedly different between Thoroughbred horses and pony breeds in autumn. These findings emphasise that breed should be accounted for when determining and interpreting reference intervals for ACTH concentrations among healthy horses and ponies in autumn.

123 US senior horses: Prevalence of medical conditions and routine preventative veterinary care

Although senior horses (aged ≥ 15 years) account for up to one-third of the equine population, information regarding their health and management is currently limited in the US To address this gap, we conducted a US-wide survey with senior horse owners. The present project is a subsection of this study with the objectives to 1) determine the prevalence of medical conditions in senior horses, 2) assess the frequency of routine preventative veterinary care (RPVC) for senior horses, and 3) identify risk factors for lack of RPVC. The anonymous survey was distributed through a press-release and social media channels and was online from Oct. 15th to Nov. 21st, 2020. Of 2927 started surveys, 2717 were eligible for analysis. Disease-prevalence estimates were calculated from response frequencies. For each RPVC frequency category (0, 1–2, ≥ 3 times/year) responses were counted and expressed as percentages. Risk factors for lack of RPVC were determined by binomial logistic regression, with P ≤ 0.05 indicating statistical significance. The top 5 veterinary-diagnosed medical conditions reported to affect horses at the time of the survey were: osteoarthritis 29.8%, dental disorders 14.8%, lameness 13.9%, pituitary pars intermedia dysfunction 11.8%, and ocular disorders 6.0% (n = 2433 total responses to question). The 5 most reported non-veterinary diagnosed (i.e., self-diagnosed, farrier-diagnosed, etc..)medical conditions were: osteoarthritis 10.8%, lameness 4.5%, dental disorders 3.3%, abscess 2.3%, and gastric ulcers 1.9% (n = 2247). Overall, 36.0% of owners stated that their horse did not have any veterinary-diagnosed medical conditions (n = 2433), while 28.6% reported that their horse had no veterinary or non-veterinary diagnosed condition (n = 2236). Most horses had received RPVC 1–2 times during the year before the survey (75.5%), while 14.3% had received RPVC more frequently, and 10.2% never during that year (n = 2402). The risk of no RPVC during the year before the survey was significantly higher for pleasure, semi-retired, and retired horses when compared with competition horses (P < 0.05) and was also higher in retired horses compared with pleasure horses (P < 0.05). In conclusion, about 2-thirds of senior horses were reportedly affected by at least one veterinary-diagnosed medical condition, with osteoarthritis being the condition most frequently reported. Diagnosis for medical conditions was predominantly made by veterinarians and rarely by other individuals. While most horses had received at least one RPVC visit during the year before the survey, retired senior horses were at a particularly high risk of not having received any RPVC that year.

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.