C. M. McGowan

Equine laminitis: induced by 48 h hyperinsulinaemia in Standardbred horses.

REASONS FOR PERFORMING STUDY Hyperinsulinaemia is known to induce laminitis experimentally in healthy ponies with no history of the condition. Horses are more insulin sensitive than ponies and whether prolonged hyperinsulinaemia and euglycaemia would have a similar laminitogenic effect requires study. OBJECTIVES To determine if laminitis results when the prolonged euglycaemic hyperinsulinaemic clamp technique (p-EHC) is applied to clinically normal Standardbred horses, and to monitor hoof wall temperature seeking an association between vascular activity and laminitis development. METHODS Eight young, clinically normal Standardbred horses were assigned into 4 pairs and within each pair, one was assigned randomly to either treatment (n = 4) or control (n = 4) groups. Treated horses received continuous infusions of insulin and glucose until clinical signs of laminitis developed, at which point the horses were subjected to euthanasia. Control horses received an equivalent volume of a balanced electrolyte infusion for the same period. Hoof wall surface temperature (HWST) was monitored continuously throughout the experimental period. RESULTS All horses in the treatment group were calculated to have normal insulin sensitivity. All treated horses, and none in the control group, developed laminitis (P = 0.01). Pronounced digital pulses were a feature of the treatment group, while insignificant digital pulses occurred in control horses. HWST was higher and less variable in treated horses once hyperinsulinaemia was established. CONCLUSIONS Healthy Standardbred horses subjected to prolonged hyperinsulinaemia develop laminitis within 48 h, demonstrating that laminitis in horses can be triggered by insulin. POTENTIAL RELEVANCE Insulin resistance and the associated hyperinsulinaemia place horses and ponies at risk of developing laminitis. This study demonstrates a need for prompt management of the persistent hyperinsulinaemia seen in some endocrinopathies.

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

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

Prevalence, risk factors and clinical signs predictive for equine pituitary pars intermedia dysfunction in aged horses

REASONS FOR PERFORMING STUDY Equine pituitary pars intermedia dysfunction (PPID) is an ageing-related neurodegenerative disorder. The prevalence and risk factors for PPID using seasonally adjusted basal adrenocorticotropic hormone (ACTH) concentrations in aged horses have not been previously reported. OBJECTIVES To determine the prevalence, risk factors and clinical signs predictive for PPID in a population of horses aged ≥ 15 years in Queensland, Australia. METHODS Owner-reported data was obtained using a postal questionnaire distributed to an equestrian group. A subgroup of surveyed owners were visited and a veterinary physical examination performed on all horses aged ≥ 15 years. Blood samples were analysed for basal plasma alpha melanocyte-stimulating hormone (α-MSH) and ACTH concentrations, routine haematology and selected biochemistry. Aged horses with elevations above seasonally adjusted cut-off values for basal plasma ACTH were considered positive for PPID. Positive horses were compared with their aged counterparts to determine risk factors and clinical signs associated with PPID. RESULTS Pituitary pars intermedia dysfunction was prevalent in aged horses (21.2%) despite owners infrequently reporting it as a known or diagnosed disease or disorder. Numerous clinical or historical signs were associated with an increased risk of PPID in the univariable model, but only age (odds ratio (OR) 1.18; 95% confidence interval (CI) 1.11-1.25, P<0.001) and owner-reported history of hirsutism (OR 7.80; 95% CI 3.67-16.57, P<0.001) remained in the final multivariable model. There were no routine haematological or biochemical variables supportive of a diagnosis of PPID. CONCLUSIONS AND POTENTIAL RELEVANCE Pituitary pars intermedia dysfunction occurs commonly in aged horses despite under-recognition by owners. The increased risk of PPID with age supports that this is an ageing associated condition. Aged horses with clinical or historical signs consistent with PPID, especially owner-reported hirsutism (delayed shedding and/or long hair coat), should be tested and appropriate treatment instituted.

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

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

Disease prevalence in geriatric horses in the United Kingdom: Veterinary clinical assessment of 200 cases

REASONS FOR PERFORMING STUDY Geriatric horses (aged ≥ 15 years) represent a substantial proportion of the equine population, yet few studies have investigated the prevalence of diseases within this population in the UK. OBJECTIVES To describe the findings of veterinary clinical examination of 200 geriatric horses and ponies in north west England and north Wales, and to assess the effect of animal age and type (horse or pony) on the presence or absence of clinical signs and veterinary diagnosed health problems. METHODS From responses to a cross-sectional postal questionnaire survey of owners of geriatric horses (n = 918/1144), 200 horses were randomly selected to receive a veterinary clinical examination covering the major body systems. RESULTS Twenty-six percent of animals were overweight (body condition score, BCS, >3/5) and 4.5% were underweight (BCS <2/5). Seventy-one percent had a dermatological abnormality and 22% displayed hirsutism or abnormal moulting. Ophthalmic lesions frequently identified included vitreous degeneration (66.0%), cataracts (58.5%) and senile retinopathy (33.7%). The prevalence of cardiac murmurs was 20%. Whilst only 7.5% of animals had a spontaneous cough during the examination, 18.5% had some form of nasal discharge and 22% had abnormalities on thoracic auscultation at rest. Following rebreathing, 13.6% developed marked abnormalities consistent with lower airway disease. When assessed at walk, 18.6% were lame on at least one limb, while 50.5% were lame in trot. The majority of animals (83.5%) had a reduction in range of motion in at least one joint. Eighty percent of animals had hoof abnormalities. Dental abnormalities were identified in 95.4% of animals, with cheek teeth diastemata, excessive wear/cupped out teeth and focal overgrowths the most frequently identified conditions. CONCLUSIONS AND POTENTIAL RELEVANCE This study has identified many prevalent clinical signs of disease in geriatric horses. Description of the most prevalent health problems and further identification of risk factors for these conditions will aid in targeted improvements in veterinary care, owner education and welfare.

Seasonal variation in serum concentrations of selected metabolic hormones in horses.

BACKGROUND Determination of adrenocorticotropic hormone (ACTH) concentration is a commonly used test in the evaluation of endocrine causes of equine laminitis, but the concentration in healthy horses can be high at certain times of year, which alters the specificity of the ACTH test. OBJECTIVE To determine if circulating concentrations of ACTH, cortisol, glucose, insulin, and thyroxine vary month to month in healthy horses and in horses with equine metabolic syndrome (EMS). ANIMALS Nine healthy adult horses were studied on their farm/stable over the course of 1 year. After the diagnosis of EMS, 10 laminitic horses residing at the same farm/stable were also studied. METHODS Prospective study of healthy and laminitic horses. Plasma/serum samples were analyzed for concentrations of hormones and glucose. RESULTS ACTH was the only analyte to show a discrete seasonal pattern, with concentrations in healthy and EMS horses frequently outside of the reference range (9-35 pg/mL) in August through October. Insulin was elevated (>40 microIU/mL) in EMS horses during most months and median serum glucose was generally higher in EMS horses (100 mg/dL, range, 76-163 mg/ dL) than in controls (94 mg/dL, range, 56-110 mg/dL), but no seasonal patterns for insulin or glucose were found. CONCLUSIONS AND CLINICAL IMPORTANCE An increased ACTH concentration in horses in late summer or autumn should be interpreted with caution. In contrast, insulin concentration is maintained within the reference range throughout the year in healthy horses, thus an increased insulin concentration at any time of year should raise suspicions of EMS, ECD, or both.

A cross-sectional study of geriatric horses in the United Kingdom. Part 1: Demographics and management practices

REASONS FOR PERFORMING STUDY With growing numbers of aged horses, geriatric medicine is becoming increasingly important in equine veterinary practice; however, there is a paucity of information on the UK equine geriatric population. OBJECTIVES To describe the demographic characteristics of the equine geriatric population and to assess management practices undertaken by owners of geriatric horses (aged≥15 years). METHODS A cross-sectional study was conducted, surveying a randomly selected sample of veterinary registered owners with horses aged≥15 years, using a self-administered postal questionnaire. RESULTS Horses aged≥15 years represented 29% of the equine population in the study area. The response rate to the questionnaire survey was 80.2%. Management practices were similar to those previously described for the general equine population. However, the level of exercise and feeding practices changed significantly with increasing age. A summary of the demographic characteristics, feeding and management of horses in a sample of the geriatric equine population is presented. CONCLUSIONS AND POTENTIAL RELEVANCE The management of geriatric horses has a direct effect on their health and welfare and this study has provided valuable information on the demographics and management of geriatric horses and ponies in the UK. The information can be used to form targeted owner education programmes for geriatric health and should aid in the investigation and prevention of disease.

Incidence and risk factors for exertional rhabdomyolysis in thoroughbred racehorses in the United Kingdom.

Telephone surveys of 34 racing yards with 1276 horses in training were made to establish the overall incidence of exertional rhabdomyolysis in the previous year. A case-control study was used to investigate the risk factors for the syndrome in 12 yards selected on the basis of the routine confirmation of diagnoses by the evaluation of the serum activities of creatine kinase and aspartate aminotransferase. The overall incidence of the syndrome was 6.7 per cent and 80 per cent of the trainers had at least one affected horse. In 74 per cent of the affected horses it frequently recurred, with an average of six lost training days per episode. Risk factors identified for the syndrome included being female, having a nervous, excitable temperament, and being two years old.

A cross‐sectional study of geriatric horses in the United Kingdom. Part 2: Health care and disease

REASONS FOR PERFORMING STUDY Geriatric horses (aged≥15 years) represent a substantial proportion of the equine population, yet very few studies have investigated the prevalence of diseases within the UK equine geriatric population. OBJECTIVES To describe the provision of routine preventive health care measures, prevalence of clinical signs of disease and the prevalence of owner reported diseases. Additionally, the effect of increasing age on the provision of preventive health care and the presence or absence of clinical signs and disease was assessed. METHODS A cross-sectional study was conducted, surveying a randomly selected sample of veterinary registered owners with horses aged≥15 years, using a self-administered postal questionnaire. RESULTS As geriatric horses increased in age, there was a reduction in the provision of preventive health care measures, such as vaccination, farrier care and routine veterinary checks. Only 68.7% of horses had received a routine veterinary visit within the previous 12 months. Owners frequently observed clinical signs in their animals, with 77% reporting at least one clinical sign of disease. Increasing age was associated with increased reporting of many clinical signs of disease. Over half (58%) of horses had at least one episode of disease within the previous 12 months, yet only 31% of owners reported that their animal currently suffered from a known disease or disorder. CONCLUSIONS AND POTENTIAL RELEVANCE Although owners frequently observed clinical signs in their aged horse, there may be incorrect or under recognition of many diseases and health problems. Reduced frequency of routine preventive health care measures, along with suboptimal owner recognition of health and welfare problems may lead to compromised welfare in the geriatric population.

Efficacy of trilostane for the treatment of equine Cushing's syndrome

REASONS FOR PERFORMING STUDY Trilostane, a competitive 3-beta hydroxysteroid dehydrogenase inhibitor, has been used successfully to control clinical signs and cortisol excess in canine pituitary dependent hyperadrenocorticism. OBJECTIVES Trilostane was evaluated for its efficacy in resolving clinical and clinicopathological abnormalities of equine Cushings syndrome (ECS) and to assess its safety. METHODS Twenty horses (mean age 21 years) diagnosed with ECS were followed for 1 or 2 years. Affected horses received 0.4-1 mg/kg (mean 0.5 mg/kg) trilostane once daily. RESULTS Clinical signs assessed over 1 or 2 years, showed a reduction in lethargy in all horses post treatment. Polyuria and/or polydipsia, present in 11 horses, was reduced in all after treatment. Recurrent or chronic laminitis, present in 16 horses, improved in 13/16 (81%) of cases. There were no side effects reported. Combined dexamethasone suppression and thyrotropin releasing hormone (TRH) stimulation tests were significantly different before and 30 days following therapy. There was a significant reduction (P = 0.01) of cortisol following TRH administration before (160 +/- 53.0 nmol/l) and after (130 +/- 46.1 nmol/l) trilostane. CONCLUSIONS Trilostane caused improvement in clinical signs in horses, without side effects, and a corresponding decrease in cortisol response to TRH administration. POTENTIAL RELEVANCE Trilostane may be a useful therapy for the treatment of ECS. Further work comparing the effects of trilostane and pergolide is warranted.