Dr. Stephen M. Reed

Metabolic and Endocrine

Funk RA, Stewart AJ, Wooldridge AA, et al.  Seasonal changes in plasma adrenocorticotropic hormone and α-melanocyte-stimulating hormone in response to thyrotropin-releasing hormone in normal aged horses. J Vet Intern Med 2011;25:579-585.

Take Home Message: Pituitary pars intermedia dysfunction (PPID) is the most common endocrine disorder of geriatric horses.  Horses with PPID have increased endogenous plasma concentrations of ACTH, α-MSH, Cortisol and Insulin; however, high variability exists in endogenous hormone concentrations complicating diagnostic testing (wide reference ranges and narrow differences between normal and affected horses).  IV administration of Thyrotropin releasing hormone in horses increases ACTH and α-MSH within 30 minutes. Thus using specific seasonal reference ranges for TRH-stimulated ACTH and α-MSH concentrations may identify subclinically affected horses and lead to improved management and treatment of horses with PPID.

McFarlane D, Paradis MR, Zimmel D, et al.  The effect of geographic location, breed, pituitary dysfunction on seasonal adrencorticotropin and α-melanocyte-stimulating hormone plasma concentrations in horses.  J Vet Intern Med 2011;25:872-881.

Take Home Message: Diagnosis of PPID in horses relies on dynamic testing such as dexamethasone suppression test or thyrotropin releasing hormone stimulation, domperidone stimulation or measurement of plasma concentrations of pituitary hormones.  These investigators demonstrated that geographic location of residence affects the onset and amplitude of the seasonal increase pars intermedia hormones. Fall increase begins earlier in horses residing farther north and a greater amplitude in seasonal hormone variation occurs in horses residing farther south. Thus seasonal and photoperiod reference ranges are needed when interpreting pars intermedia hormones in horses and may be helpful for early recognition of PPID in horses. 

Copas S, Durham AE. Circannual variation in plasma adrenocorticotropic hormone concentrations in the UK in normal horses and ponies, and those with pituitary pars intermedia dysfunction. Equine Vet J doi: 10.1111/j.2042-3306.2011.00444.x

This article represents a Paradigm shift because we have all been taught that due to the seasonal variation in pars intermedia hormone concentrations the time to not test was in the fall.  However, this study demonstrated that because of this variation in hormone concentrations year round the fall turns out to be the best time to test.

Chameroy KA, Frank N, Elliott SB, et al.  Effects of a supplement containing chromium and magnesium on morphometric measurements, resting glucose, insulin concentrations and insulin sensitivity in laminitic obese horses. Equine Vet J 43(4):494-499.

Take Home Message: Feeding chromium and magnesium failed to alter morphometric measurements, blood variables, resting insulin concentrations or insulin sensitivity in obese previous laminitic horses.

Fielding CL, Meier CA, Balch OK, et al.  Risk factors for the elimination of endurance horses from competition.  J Am Vet Med Assoc 2011;239(4):493-498. 

Take Home Message:  Endurance horses compete over distances from 40 to 160 km in a 24 hour period with elimination rates between 10 to 60% depending on the course and speed.  Horses are eliminated for either lameness, metabolic derangements, such as high heart rate with failure to recover or impending medical condition or time faults or rider elects to stop.  These authors examined the performance of 3,493 horses with 14,490 veterinary examinations and demonstrated that horses with higher body mass index (Appaloosa and QH) over 6 years of age and on longer rides have the greater likelihood of being eliminated.  Three important variables appear to be prolonged capillary refill time, reduced gut sounds, and lack of a recording.  Veterinarians may be hesitant to write down an abnormal finding thus allowing a horse with an impending problem to continue in competition.

Waller AP, Burns TA, Mudge MC, et al. Insulin resistance selectively alters cell-surface glucose transporters but not their total protein expression in equine skeletal muscle. J Vet Intern Med 2011;25(2):315-321.

Take Home Message:  These results suggested that IR in horses affects the glucose transport pathway through impairment of GLUT4 trafficking by selectively decreasing the content of basal active cell-surface GLUT4.  Having a detailed understanding of the mechanisms responsible for impaired glucose transport is important for veterinarians to find pharmacological interventions for horses affected with IR and metabolic syndromes.  To date, very few medications utilized for treatment of diabetes in humans have been critically evaluated in horses.

Respiratory and Cardiovascular

Koblinger K, Nicol J, McDonald K, et al.  Endoscopic assessment of airway inflammation in horses. J Vet Intern Med 2011;25(5):1118-1126.   

Take Home Message:  the upper and lower airway inflammation in horses appears to not follow the notion of “one-airway, one disease” concept similar to what has been described for humans.  The authors scored 128 horses with regard to pharyngitis, pharyngeal mucus, tracheal mucus, tracheal septum thickness and bronchial mucus and found that the lower airway scores but not the upper airway scores were significantly increased in horses with severe inflammation in the BAL fluid.  Thus, unlike in people where presence of rhinitis and sinusitis are often found in people with asthma and COPD similar findings do not appear to occur in horses.

Lyle CH, Uzal FA, McGorum BC, et al.  Sudden death in racing Thoroughbred horses: An international multicentre study of post mortem findings. Equine Vet J 2011:43(3):324-331.

Take Home Message:  The authors examined 268 cases of sudden death in racing Thoroughbreds from 6 racing jurisdictions around the world and in only 53% of the deaths were they able to identify a definitive cause of death.  Although in another 25% of horses they were able to identify a presumptive cause of death, leaving 22% of horses experiencing sudden death unexplained.  To me this was a very valuable study because it demonstrates the similarity of lesions resulting in exercise related sudden death from different racing jurisdictions and because it emphasizes the need for careful physical examinations including cardiac and cardiopulmonary assessment by veterinarians at the racetrack.

Dauvillier J, Felippe MJB, Lunn DP, et al. Effect of long-term fluticasone treatment on immune function in horses with heaves. J Vet Intern Med 2011;25:549-557.

Take Home Message: These and other authors have previously demonstrated that use of corticosteroids is currently the most effective pharmacological treatment of heaves in horses.  The concern of both owners and veterinarians has been what possible impact prolonged use of these medications might have on the humoral and/or cell mediated immunity of horses.  Damage to the immune system has been demonstrated in humans.  This study demonstrated that use of inhaled fluticasone at proper doses for 11 months had no significant detectable effect on the immune systems of the horses.  The authors suggest that prolonged administration would not compromise the immune response to either pathogens or vaccinations.

Gildea S, Artkins S, Cullinane A.  Management and environmental factors involved in equine influenza outbreaks in Ireland: 2007-2010.  Equine Vet J 2011;43(5):606-617.

Take Home Message: Equine influenza remains an important equine respiratory disease primarily because of the significant expense associated with the rapid spread and loss of training and racing or showing time in horses.  Risk factors include the contagiousness of the virus, the short incubation period, the dramatic hacking cough that allows for rapid spread of the virus.  Control measures should include prompt isolation of suspected cases, rapid diagnostic testing including RT-PCR of nasal swabs, maintenance of good vaccination protocols and implementation of biosecurity measures to avoid transmission by fomites and personnel.

Vengust F, Kerr C, Staempfli HR, et al.  Effect of frusemide on transvascular fluid fluxes across the lung in exercising horses.  Equine Vet J 2011;43(4):451-459.

Take Home Message:  Giving 250 mg of furosemide (Salix) 4 hours prior to exercise at 80% of VO₂  max did not change exercise performance, had no effect on erythrocyte volume regulation across the alveolar capillary barrier, and did not affect transvascular fluid fluxes in pulmonary circulation despite decreasing cardiac output.  These findings indicate that administration of furosemide at a dose of 250 mg had no effect on erythrocyte and transvascular fluid fluxes across the lung during exercise in horses and thus at this dose may not be an effective treatment for regulating transvascular forces during exercise, although it may still be an effective treatment of EIPH.

Wasko AJ, Barkema HW, Nicol J, et al.  Evaluation of a risk screening questionnaire to detect equine lung inflammation: Results of a large field study. Equine Vet J 2011;43(2):145-152.

Take Home Message:  In both North America and Europe two types of inflammatory respiratory diseases are observed: recurrent airway obstruction and inflammatory airway disease.  The best diagnostic technique to identify and separate these conditions is by use of bronchoalveolar lavage. This testing requires some sophisticated equipment as well as specialized staining and ability to interpret the findings.  These authors demonstrated that by proper use of a validated risk screening questionnaire they were able to screen for horses with lower airway inflammation, but the testing was not sophisticated enough to separate horses between mild to moderate versus severe lower airway inflammation or between mild and normal. Indicating the benefit of the RSQ as a screening tool but to diagnose either RAO or IAD you need to perform a BAL.  

Useful Diagnostic Techniques in Equine Medicine

Tyner GA, Nolen-Watson RD, Hall T, et al.  A multicenter retrospective study of 151 renal biopsies in horses. J Vet Intern Med 2011;25:532-539.

Take Home Message:  Renal biopsy is a fairly common procedure in both human and veterinary medicine. In the past, this condition has been suggested to have a high rate of complications associated with its performance.  These authors examined 151 biopsies from 146 horses and showed a low complication rate and a good correlation between the biopsy results and post-mortem findings when both were available. Interestingly, in many cases the information from the biopsy was often more detailed than the findings on post-mortem.  The one disappointment from the study was the fact that the authors were unable to determine the usefulness of the biopsy in altering the management of the patient.

Underwood C, et al. Echocardiographic changes in heart size in hypohydrated horses. J Vet Intern Med 2011;25:563-569.

Take Home Message:  Hypohydration (5-7% BW) produces echocardiographic changes that may mask changes in cardiac chamber size that occur secondary to valvular regurgitation, obscure proper evaluation of dilated cardiomyopathy, and could confound the evaluation of echocardiographic prediction of athletic performance.  The use of echocardiography in horses to measure relative wall thickness of the left ventricle was a useful noninvasive technique to monitor volume status and response to fluid therapy in horses, even with a single measurement. The authors warn that hypohydration could result in alteration of variables often applied to predict potential athletic in a horse.

Winjberg ID, et al. Quantitative motor unit action potential analysis in 2 paraspinal neck muscles in adult royal Dutch sport horses. J Vet intern Med 2011;25:592-597.

Take Home Message:  Over the past 10 years it has become common to diagnose cervical problems as a cause of poor performance in horses.  In many horses the diagnosis is based on clinical assessment and interpretation of cervical vertebral radiographs. However, use of quantitative EMG in human medicine for diagnosis of some movement disorders has been shown to be helpful since the 1950s. The authors have shown usefulness of this technique in evaluation of horses with stringhalt as well as with suspected cervical lesions. In this paper they seek to establish normal values to use for the diagnosis of horses with cervical neurogenic disorders.  The recognition of cervical radiculopathies may be very helpful to diagnose neck problems in horses.

Aleman M, Williams DC, Jorge NE, et al. Repetitive stimulation of the common peroneal nerve as a diagnostic aid for botulism in foals. J Vet Intern Med 2011;25:365-372.

Take Home Message:  Botulism is an important clinical problem in foals.  The biggest challenge facing veterinarians with cases of suspected botulism is how to make an accurate diagnosis in order to advise owners about potentially beneficial but expensive therapies. The authors demonstrate a technique to help with early recognition of this problem in order to institute early, effective treatment. Although this technique may not be immediately available to all practitioners it is important to be aware of this serious and sometimes fatal disease affecting foals.

Internal Medicine Problems Affecting the Gastrointestinal Tract of Horses

Marshall JF, Blickslager AT. The effect of nonsteroidal anti-inflammatory drugs on the equine intestine.  Equine Vet J 2011;43:140-144.

Take Home Message:  The use of nonsteroidal anti-inflammatory medications on horses for the treatment of endotoxemia and more often for the management of pain is common.  The recognition of typical side effects such as gastric ulceration and right dorsal colitis has been reported. The author’s show that use of NSAIDs with cyclooxygenase independent anti-inflammatory effects or a COX-2 selective mode of action may achieve the same benefits with fewer side effects.

Dunkel B, Chaney KP, Dallap-Schaer BL, et al.  Putative intestinal hyperammonemia in horses: 36 cases. Equine Vet J 2011;43(2):133-140.

Take Home Message:  The recognition of neurological signs in horses presented for diarrhea, colic, colitis or enteritis should not be a surprise to practitioners examining horses with these problems.  In addition to the expected clinical signs and laboratory findings such as a high heart rate, increased packed cell volume and increased blood lactate and blood glucose, these horses may also have high blood ammonia concentrations leading to neurological signs.  This can be very important as some horses with clinical signs indicative of diffuse cerebral disease may have a primary gastrointestinal problem. 

Page, A et al. Adaptation and validation of a bacteria-specific ELISA for determination of farm-specific Lawsonia intracellularis seroprevalence in Kentucky Thoroughbreds.  Equine Vet J 43;(Suppl. 40):25-31.

Take Home Message: Lawsonia intracellularis was reported to be an emerging cause of hypoproteinemia and gastrointestinal upset in weanlings foals last year. Work in Dr. Horohov’s as well as other laboratories has demonstrated this disease to be increasing in frequency. The work by Page et al shows that in central Kentucky the problem may have specificity to individual farms.