Anna M. Firshman

Factors affecting clinical assessment of insulin sensitivity in horses

Insulin resistance is thought to be involved in the pathogenesis of many equine conditions such as pars intermedia dysfunction, equine metabolic syndrome, diabetes mellitus, hyperlipaemia, laminitis, endotoxaemia and osteochondrosis dissecans (OCD); whereas polysaccharide storage myopathy in Quarter Horses and equine motor neuron disease (EMD) have been associated with increased insulin sensitivity. However, it is clear that there is not one ideal test, in terms of both practicality and accuracy, for evaluating insulin sensitivity in horses and improved diagnostic techniques are required. This review sets out the background to the subject and identifies current knowledge regarding the measurement of insulin sensitivity by tolerance testing and clamping techniques. Factors affecting insulin sensitivity, such as breed, pregnancy, lactation, obesity and nutritional factors are discussed. In addition, the relationship with training, nutritional supplementation and drug administration are considered.

Pharmacokinetics and bioavailability of metformin in horses

OBJECTIVE To determine pharmacokinetics and oral bioavailability of metformin in healthy horses. ANIMALS 4 adult horses. PROCEDURES 6 g of metformin was administered 3 times IV and PO (fed and unfed) to each horse, by use of a crossover design, with a 1-week washout period between treatments. Plasma metformin concentration was determined via high-pressure liquid chromatography. RESULTS Mean +/- SD distribution half-life of metformin following IV administration was 24.9 +/- 0.4 minutes with a volume of distribution of 0.3 +/- 0.1 L/kg. Mean area under the curve was 20.9 +/- 2.0 h.microg/mL for IV administration; PO administration resulted in area under the curves of 1.6 +/- 0.4 h.microg/mL in unfed horses and 0.8 +/- 0.2 h.microg/mL in fed horses. Bioavailability was determined to be approximately 7.1 +/- 1.5% in unfed horses and 3.9 +/- 1.0% in fed horses. The maximal concentration following PO administration in unfed horses was 0.4 +/- 0.1 microg/mL with a time at maximal concentration of 0.9 +/- 0.1 hours. In fed horses, maximal concentration was reduced to 0.3 +/- 0.04 microg/mL with a time at maximal concentration at 1.3 +/- 0.3 hours. CONCLUSIONS AND CLINICAL RELEVANCE The low bioavailability of metformin may explain the reported lack of clinical success in improving insulin sensitivity with metformin treatment in horses. Dosages and dose intervals previously used may have been insufficient to achieve plasma concentrations of drug comparable to the therapeutic range achieved in humans. Therefore, a larger and more frequently administered dose may be required to fully evaluate efficacy of metformin in horses.

Comparison of Histopathologic Criteria and Skeletal Muscle Fixation Techniques for the Diagnosis of Polysaccharide Storage Myopathy in Horses

The purpose of the study reported here was to determine the effect of three methods of fixation of skeletal muscle biopsy specimens on the histopathologic appearance of muscle sections and to determine criteria that were most consistently associated with a diagnosis of polysaccharide storage myopathy (PSSM) in horses. Surgically excised semimembranosus muscle biopsy specimens were obtained from nine horses previously diagnosed with PSSM and from 15 control horses. Portions of each specimen were fixed in formalin, frozen immediately, and chilled for 24 hours prior to freezing. Sections stained with hematoxylin and eosin (HE), periodic acid-Schiff (PAS), and amylase-PAS were scored for histopathologic criteria by three investigators blinded to the sample origin. The presence of amylase-resistant, abnormal polysaccharide was found to be the most sensitive and specific diagnostic indicator for PSSM, and was readily detected regardless of the fixation technique or investigator. Other less-specific features associated with PSSM included atrophy and cytoplasmic and subsarcolemmal vacuoles; however, their histologic scores varied among fixation technique and investigators. Scores for subsarcolemmal and cytoplasmic amylase-sensitive glycogen in horses with PSSM were similar to those for control horses and varied among fixation techniques. In conclusion, PSSM is most accurately diagnosed in muscle biopsy specimens on the basis of appearance of amylase-resistant, abnormal polysaccharide, not amylase-sensitive glycogen, regardless of fixation technique. In general, frozen sections appeared to be better suited for studying myopathies because many histopathologic features of skeletal muscle were obscured by formalin fixation.

Cryptosporidiosis in 20 alpaca crias

CASE DESCRIPTION 20 alpaca crias (13 females and 7 males) were examined for diarrhea (n=20), weight loss (15), and poor appetite (5). Fourteen crias were between 8 and 18 days of age at time of admission. CLINICAL FINDINGS Cryptosporidiosis was diagnosed in all crias. Common biochemical abnormalities included acidemia, hyperlactemia, azotemia, and hyperglycemia and increases in aspartate transaminase and gamma-glutamyltransferase activities. Serum sodium and chloride concentrations were high or low. Other potential gastrointestinal tract pathogens were identified in only 7 crias. TREATMENT AND OUTCOME Supportive care was instituted, including i.v. administration of fluids with partial parenteral administration of nutrients (n=19 crias), antimicrobials (19), supplemental orally administered nutrients (11), administration of plasma (10), and insulin treatment (9). Other palliative treatments used by attending clinicians were sucralfate, flunixin meglumine, vitamin A/D/E/B complex, antiparasitic agents, antidiarrheal agents, and azithromycin. Three crias with inadequate urine production and severe azotemia were treated with furosemide administered i.v. as a bolus or as a constant-rate infusion. Treatment resulted in a successful outcome in 16 of 20 crias. Weight loss and refractory azotemia were common in nonsurvivors but not in surviving crias. CLINICAL RELEVANCE Findings suggested that Cryptosporidium spp may be a diarrheal pathogen of unweaned alpaca crias that may be more widespread than has been recognized and can become endemic on some farms. Metabolic derangements were unpredictable and should be determined by biochemical analysis before fluid and electrolyte replacement is initiated. Cryptosporidiosis has zoonotic potential, and the infection can be self-limiting in alpacas receiving supportive treatment.

Insulin sensitivity in Belgian horses with polysaccharide storage myopathy

OBJECTIVE To determine insulin sensitivity, proportions of muscle fiber types, and activities of glycogenolytic and glycolytic enzymes in Belgians with and without polysaccharide storage myopathy (PSSM). ANIMALS 10 Quarter Horses (QHs) and 103 Belgians in which PSSM status had been determined. PROCEDURES To determine insulin sensitivity, a hyperinsulinemic euglycemic clamp (HEC) technique was used in 5 Belgians with PSSM and 5 Belgians without PSSM. Insulin was infused i.v. at 3 mU/min/kg for 3 hours, and concentrations of blood glucose and plasma insulin were determined throughout. An i.v. infusion of glucose was administered to maintain blood glucose concentration at 100 mg/dL. Activities of glycogenolytic and glycolytic enzymes were assessed in snap-frozen biopsy specimens of gluteus medius muscle obtained from 4 Belgians with PSSM and 5 Belgians without PSSM. Percentages of type 1, 2a, and 2b muscle fibers were determined via evaluation of >or= 250 muscle fibers in biopsy specimens obtained from each Belgian used in the aforementioned studies and from 10 QHs (5 with PSSM and 5 without PSSM). RESULTS Belgians with and without PSSM were not significantly different with respect to whole-body insulin sensitivity, muscle activities of glycogenolytic and glycolytic enzymes, or proportions of muscle fiber types. However, Belgians had an increased proportion of type 2a and decreased proportion of type 2b muscle fibers, compared with proportions in QHs, regardless of PSSM status. CONCLUSIONS AND CLINICAL RELEVANCE PSSM in Belgians may be attributable to excessive glycogen synthesis rather than decreased glycogen utilization or enhanced glucose uptake into muscle cells.

Effect of water depth on amount of flexion and extension of joints of the distal aspects of the limbs in healthy horses walking on an underwater treadmill

OBJECTIVE To determine the maximum amount of flexion and extension of the carpal, tarsal, metacarpophalangeal, and metatarsophalangeal joints and the percentage duration of the stance and swing phases of the stride for horses walking on an underwater treadmill in various water depths. ANIMALS 9 healthy adult horses. PROCEDURES Zinc oxide markers were placed on the forelimbs and hind limbs of the horses. Video was recorded of horses walking (0.9 m/s) on an underwater treadmill during baseline conditions (< 1 cm of water) or in various amounts of water (level of the metatarsophalangeal, tarsal, and stifle joints). Maximum amount of joint flexion and extension, range of motion (ROM), and the percentage durations of the stance and swing phases of the stride were determined with 2-D motion analysis software. RESULTS The ROM was greater for all evaluated joints in any amount of water versus ROM for joints in baseline conditions (primarily because of increases in amount of joint flexion). The greatest ROM for carpal joints was detected in a tarsal joint water depth, for tarsal joints in a stifle joint water depth, and for metacarpophalangeal and metatarsophalangeal joints in metatarsophalangeal and tarsal joint water depths. As water depth increased, the percentage durations of the stance and swing phases of the stride significantly decreased and increased, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results of this study suggested that exercise on an underwater treadmill is useful for increasing the ROM of various joints of horses during rehabilitation and that the depth of water affects the amount of flexion and extension of joints.

The effect of agility exercise on eicosanoid excretion, oxidant status, and plasma lactate in dogs

BackgroundThe objective was to determine the effects of agility exercise on dogs of different skill levels with respect to urinary eicosanoids, urinary 15F2t-isoprostane (lipid peroxidation marker) and hematological/biochemical changes in plasma. Fifteen adult dogs had blood and urine samples obtained prior to, immediately and 4-hours following an agility exercise.ResultsHematocrit, red blood cells (RBC), albumin, and hemoglobin increased following exercise, with greatest increases correlating to increased skill group (novice, intermediate, masters); at 4-hours post-exercise, hematocrit, RBC, and hemoglobin were decreased. Phosphorus increased following exercise with the greatest increase in novice and intermediates. Plasma lactate increased 3.6-fold in masters, 3.2-fold in intermediates, and 1.2-fold in novice dogs. Urine thromboxane B2 (TXB2) more than tripled 4-hours post-exercise while 6-keto prostaglandin F1α (PGF1α, prostacyclin metabolite), prostaglandin E2 metabolites (13,14-dihydro-15-keto-prostaglandin A2 and 13,14-dihydro-15-keto-prostaglandin E2), and 13,14-dihydro-15-keto prostaglandin F2α were unaffected as determined by a competitive enzyme immunoassay and standardized by division with urine creatinine. Urine 15F2t-isoprostane increased insignificantly.ConclusionsAlterations in the plasma post-exercise were likely due to hemoconcentration from insensible water loss, splenic contraction and sympathetic stimulation while 4-hours later autohemodilution reduced RBC parameters. Elevations in plasma lactate and urinary TXB2 correlated with advanced skill level/speed of the dogs.

Histopathologic findings in the sacrocaudalis dorsalis medialis muscle of horses with vitamin E-responsive muscle atrophy and weakness

OBJECTIVE To characterize clinical findings, outcomes, muscle characteristics, and serum or muscle concentrations of α-tocopherol for horses with vitamin E-responsive signs of muscle atrophy and weakness consistent with signs of equine motor neuron disease (EMND). DESIGN Retrospective case-control study. ANIMALS 8 affected (case) adult horses with acute (n = 3) or chronic (5) gross muscle atrophy that improved with vitamin E treatment and 14 clinically normal (control) adult horses with adequate (within reference range; 8) or low (6) muscle concentrations of α-tocopherol. PROCEDURES Medical records were reviewed, serum and muscle concentrations of α-tocopherol were measured, and frozen biopsy specimens of sacrocaudalis dorsalis medialis muscle and gluteal muscle were histologically evaluated for pathological changes. Fiber type composition and fiber diameters were assessed in gluteal muscle specimens. RESULTS A myopathy that was histologically characterized by redistribution of mitochondrial enzyme stain (moth-eaten appearance) and anguloid atrophy of myofibers was evident in sacrocaudalis dorsalis medialis muscle fibers of the 8 affected horses that had low serum (6/8) or skeletal muscle (5/5) concentrations of α-tocopherol; these histopathologic changes were not found in muscle specimens of control horses with low or adequate muscle concentrations of α-tocopherol. All affected horses regained strength and muscle mass within 3 months after initiation of vitamin E treatment and dietary changes. CONCLUSIONS AND CLINICAL RELEVANCE A vitamin E-deficient myopathy characterized histologically by a moth-eaten appearance in the mitochondria and anguloid myofiber atrophy in frozen sections of sacrocaudalis dorsalis medialis muscle biopsy specimens was found in horses with clinical signs of EMND that were highly responsive to vitamin E treatment. This myopathy may be a specific syndrome or possibly precede the development of neurogenic muscle fiber atrophy typical of EMND.

Thrombotic Endocarditis in 10 Alpacas

BACKGROUND A description of the clinical signs and necropsy findings in 10 alpacas with thrombotic endocarditis. ANIMALS Clinical cases admitted to 2 veterinary referral hospitals between May 1998 and December 2006. METHODS A retrospective study was performed by searching hospital records to identify alpacas diagnosed with endocarditis. RESULTS Common clinical findings included sternal recumbency, tachycardia, tachypnea, and abdominal distension. Heart sounds were recorded as normal in 7 of 10 alpacas. Pleural and pericardial effusion and ascites were often present. Complete blood cell counts often suggested inflammation, and liver enzyme activity was often increased. When echocardiography was performed, a soft tissue density was imaged within the right ventricle. All alpacas died or were euthanized. Necropsy revealed mural endocarditis with right ventricular or biventricular fibrinous thrombi obliterating the ventricular lumina with no valvular involvement in 6 of 10 affected animals. Bacteria were not consistently identified as a cause for the endocarditic lesions. Eight of the 10 alpacas had evidence of hepatic fluke infestation. CONCLUSIONS AND CLINICAL IMPORTANCE Valvular and mural thrombotic endocarditis should be included in the list of differential diagnoses for hepatomegaly, abdominal distension, and other signs of right-sided congestive heart failure in alpacas. The prognosis of this disease is grave.

Optimal Diet of Horses with Chronic Exertional Myopathies

Chronic exertional rhabdomyolysis represents a syndrome of recurrent exercise-associated muscle damage in horses that arises from a variety of etiologies. Major advances have been made in the understanding of the pathophysiology of this disease, and causative genetic defects have been recently identified for two conditions-polysaccharide storage myopathy of quarter horses, paints, warm bloods, and draft breeds. Dietary management in combination with a regular exercise regimen comprises the most effective means for control of clinical signs.