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Objective—To determine the influence of age on results of quantitative analysis of electromyographic (EMG) needle examination in the subclavian, triceps, and lateral vastus muscles of Dutch Warmblood horses.
Animals—7 healthy young Dutch Warmblood horses (range, 13 to 18 months old), 7 healthy adult Dutch Warmblood horses (range, 4 to 10 years old), and 7 healthy elderly Dutch Warmblood horses (range, 18 to 21 years old).
Procedure—An EMG needle examination was performed to evaluate insertional activity, spontaneous activity, and motor unit action potential (MUAP) variables. Although all horses were conscious, young horses were sedated prior to examination.
Results—Mean insertional activity in young horses was significantly lower than in elderly horses. Pathologic spontaneous activity was rarely found in young and adult horses but was frequently evident in all muscles in all elderly horses. The MUAP duration and amplitude were significantly lower in all muscles of young horses, compared with values for adult and elderly horses. The MUAP duration and number of phases and turns were significantly lower in adult horses than in elderly horses. Group differences for percentages of polyphasic and complex MUAPs were also found. The 95% confidence intervals for MUAP duration, MUAP amplitude, and number of phases and turns for the subclavian, triceps, and lateral vastus muscles were significantly lower in young horses than in adult or elderly horses.
Conclusion and Clinical Relevance—Age of the horse being examined should be considered when EMG examination is performed. (Am J Vet Res 2003;64:70–75)
Objective—To compare the effects of administration of 2 volumes of a calcium solution (calcium oxide and calcium gluconate) on plasma ionized calcium concentration (PICaC) and clinical recovery from naturally occurring hypocalcemia (NOHC; milk fever) in lactating dairy cows.
Animals—123 cows with NOHC (PICaC < 0.95 mmol/L [3.81 mg/dL]) and 20 clinically normal control cows.
Procedures—Affected cows were treated IV once or repeatedly with 450 (n = 56) or 750 mL (67) of calcium solution (1.65 g of calcium/100 mL) until clinical recovery was achieved. The PICaC was assessed 48 hours after the first treatment or after the treatment that achieved clinical recovery. Biochemical recovery was defined as PICaC ≥ 0.95 mmol/L. Plasma from control cows was used for PICaC reference range determination. Plasma samples from both groups were assessed after storage for 20 days at 20°C.
Results—The PICaC reference range derived from blood collected in tubes containing lithium heparin was 1.02 to 1.29 mmol/L (4.09 to 5.17 mg/dL). Following storage, plasma samples were suitable for PICaC assessment. All cows treated with ≥ 1 volume of 450 and 750 mL of calcium solution recovered clinically; however, 31 of 83 (37%) evaluated cows were not biochemically recovered at 48 hours following treatment. Only cows with PICaC < 0.48 mmol/L (1.92 mg/dL) before the first treatment had to be treated ≥ 3 times.
Conclusions and Clinical Relevance—Results did not support the need to increase the administered volume of calcium solution from 450 to 750 mL for treatment of NOHC in dairy cows.
Objectives—To acquire reference range values indicative of glucose metabolism by use of the hyperglycemic clamp technique in healthy horses and evaluate the usefulness of the euglycemic hyperinsulinemic clamp technique in healthy horses and ponies.
Animals—5 Dutch Warmblood horses and 4 Shetland ponies.
Procedure—The hyperglycemic clamp technique was used for quantification of the sensitivity of beta cells to exogenous glucose infusion in horses. The euglycemic hyperinsulinemic clamp technique was used to determine the sensitivity and responsiveness of tissues to exogenous insulin in horses and ponies.
Results—During the hyperglycemic clamp technique, the mean amount of glucose metabolized (M) in horses was 0.011 ± 0.0045 mmol/kg·min–1 (95% confidence interval [CI], 0.0018 to 0.020 mmol/kg·min–1; range, 0.000035 to 0.021 mmol/kg·min–1) and the mean M value-to-plasma insulin concentration (I) ratio (ie, mmol of glucose/kg·min–1 per pmol of insulin/L X 100) was 0.017 ± 0.016 (95% CI, –0.014 to 0.049; range, 0.000025 to 0.055). During the euglycemic hyperinsulinemic clamp technique, the mean M value was 0.014 ± 0.0055 mmol/kg·min–1 (95% CI, 0.0026 to 0.025 mmol/kg·min–1; range, 0.0042 to 0.023 mmol/kg·min–1) in horses and 0.0073 ± 0.0020 mmol/kg·min–1 (95% CI, 0.0034 to 0.011 mmol/kg·min–1; range, 0.0049 to 0.011 mmol/kg·min–1) in ponies. The M value was significantly lower in ponies than in horses, whereas the M:I ratios were not significantly different between horses and ponies.
Conclusion and Clinical Relevance—Glucose clamp techniques offer good methods to investigate glucose metabolism in horses and ponies. A higher degree of insulin resistance was found in ponies, compared with Dutch Warmblood horses. (Am J Vet Res 2003;64: 1260–1264)
Objective—To determine whether electromyographic abnormalities are evident in skeletal muscles in horses with induced hypocalcemia and hypomagnesemia.
Animals—7 healthy adult Dutch Warmblood horses.
Procedure—Electromyographic examination was performed in the lateral vastus, triceps, and subclavian muscles before and after IV infusion of EDTA. An initial dose (mean ± SD, 564 ± 48 ml) of a 10% solution of sodium EDTA was administered IV during a period of 21 ± 7.3 minutes to establish a blood concentration of ionized calcium of approximately 0.5 mMol/L. Average rate of EDTA infusion to maintain ionized calcium at this concentration was 6.6 ml/min.
Results—Mean blood concentrations of ionized calcium and magnesium were 1.39 ± 0.06 and 0.84 ± 0.09 mM, respectively before EDTA infusion; after EDTA infusion, concentrations were 0.48 ± 0.05 and 0.44 ± 0.20 mM, respectively. This state induced positive waves; fibrillation potentials; doublets, triplets, and multiplets; complex repetitive discharges; and neuromyotonia. Analysis of motor unit action potentials (MUAP) after EDTA infusion revealed an increase in prevalence of polyphasic and complex MUAP in all muscles.
Conclusion and Clinical Relevance—None of the horses had classical signs of hypocalcemia and hypomagnesemia. In contrast, all horses had spontaneous activity in the measured muscles indicative of nerve hyperirritability. Calcium and magnesium deficits appear to have consequences, which may be subclinical, affecting functions of the neuromuscular system. This is of interest for equestrian sports in which hypocalcemia and hypomagnesemia are expected, such as during endurance rides. (Am J Vet Res 2002;63:849–856)
Objective—To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses.
Animals—10 healthy adult Dutch Warmblood horses.
Procedure—Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses.
Results—Mean ± SD duration of insertional activity was 471.7 ± 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 µV (95% confidence interval [CI], 349 to 410 µV). Mean MUAP duration of the subclavian muscle was 7.27 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP, defined as MUAP with > 4 phases, was 7.7%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP.
Conclusions and Clinical Relevance—This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses. (Am J Vet Res 2002;63:198–203)
Objective—To determine size and weight of the pituitary gland and associations between pituitary gland size and weight and sex and age in horses without clinical signs associated with pituitary pars intermedia adenoma (PPIA) and horses and ponies with PPIA.
Animals—Pituitary glands from 100 horses without clinical signs of PPIA and 19 horses and 17 ponies with PPIA.
Procedures—Pituitary glands were weighed, measured, and examined histologically by use of H&E stain. Masson trichrome and periodic acid-Schiff staining were used, when appropriate. Histologic lesions in the pars intermedia, pars distalis, or both were classified as no significant lesions, single or multiple cysts, focal or multifocal hyperplasia, single or multiple microadenomas, and adenoma. Relative pituitary weight (RPW) was calculated as pituitary weight (grams) divided by body weight (grams).
Results—There was an age-related increase in the presence of pituitary lesions in the pars distalis and pars intermedia in geldings, mares overall, and nonpregnant mares. Mean (± SD) RPW in horses with PPIA was not significantly different from ponies with PPIA (15 ± 5.9 X 10–6 and 16 ± 7.2 × 10–6, respectively). Maximum pituitary weight in a horse with PPIA was 13.9 g (RPW, 2.9 × 10–5). Plasma glucose concentration was positively correlated with RPW in ponies with PPIA.
Conclusions and Clinical Relevance—Pituitary lesions may be a factor in horses with insulin resistance and laminitis before development of clinical signs of PPIA. Ovarian steroids may be involved in the pathogenesis of lesions in the pars intermedia. (Am J Vet Res 2004;65:1701–1707)
Objective—To evaluate the effect of various head and neck positions on intrathoracic pressure and arterial oxygenation during exercise in horses.
Animals—7 healthy Dutch Warmblood riding horses.
Procedures—The horses were evaluated with the head and neck in the following predefined positions: position 1, free and unrestrained; position 2, neck raised with the bridge of the nose aligned vertically; position 4, neck lowered and extremely flexed with the nose pointing toward the pectoral muscles; position 5, neck raised and extended with the bridge of the nose in front of a vertical line perpendicular to the ground surface; and position 7, neck lowered and flexed with the nose pointing towards the carpus. The standard exercise protocol consisted of trotting for 10 minutes, cantering for 4 minutes, trotting again for 5 minutes, and walking for 5 minutes. An esophageal balloon catheter was used to indirectly measure intrathoracic pressure. Arterial blood samples were obtained for measurement of Pao2, Paco2, and arterial oxygen saturation.
Results—Compared with when horses were in the unrestrained position, inspiratory intrathoracic pressure became more negative during the first trot (all positions), canter and second trot (position 4), and walk (positions 4 and 5). Compared with when horses were in position 1, intrathoracic pressure difference increased in positions 4, 2, 7, and 5; Pao2 increased in position 5; and arterial oxygen saturation increased in positions 4 and 7.
Conclusions and Clinical Relevance—Position 4 was particularly influential on intrathoracic pressure during exercise in horses. The effects detected may have been caused by a dynamic upper airway obstruction and may be more profound in horses with upper airway disease.
Objective—To compare the effects of IV administration of various doses of ovine corticotrophin–releasing hormone (oCRH) on plasma and saliva cortisol concentrations in healthy horses and determine whether an oCRH challenge test protocol is valid for use in adult horses.
Animals—24 healthy Warmblood horses.
Procedures—Each horse received oCRH in saline (0.9% NaCl) via IV administration at a dose of 0 (control treatment), 0.01, 0.1, or 1.0 Mg/kg (6 horses/group). Jugular blood and saliva samples were collected simultaneously 15 minutes before and immediately prior to injection (baseline); data from these samples were pooled to provide basal values. Subsequently, 14 postinjection blood and saliva samples were both collected within a 210-minute period. Cortisol concentrations in all samples were assessed via a solid-phase radioimmunoassay.
Results—All doses of oCRH induced significant increases from baseline in both plasma and salivary cortisol concentrations. Compared with the smaller doses of oCRH, the 1.0 Mg/kg dose of oCRH induced significantly greater plasma cortisol concentrations. A relationship (r = 0.518) between basal cortisol concentrations in plasma and saliva was detected.
Conclusions and Clinical Relevance—For use as a CRH challenge test in adult horses, a protocol involving IV administration of a dose of at least 0.01 Mg of oCRH/kg and postinjection collection of blood samples from 10 to 180 minutes and saliva samples from 20 to 50 minutes for assessment of plasma and saliva cortisol concentrations should be sufficient. Application of such a test might be helpful to detect states of chronic activation of the hypothalamo-pituitary-adrenocortical axis at the hypothalamic level.
Objective—To determine the influence of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in horses and identify potential markers indicative of early overtraining.
Animals—12 Standardbred geldings.
Procedures—Horses underwent 4 phases of treadmill-based training. In phase 1, horses were habituated to the treadmill. In phase 2, endurance training was alternated with high-intensity exercise training. In phase 3, horses were divided into control and intensified training groups. In the intensified training group, training intensity, duration, and frequency were further increased via a protocol to induce overtraining; in the control group, these factors remained unaltered. In phase 4, training intensity was reduced. Standardized exercise tests were performed after each phase and hyperinsulinemic euglycemic clamp (HEC) tests were performed after phases 2, 3, and 4.
Results—10 of 12 horses completed the study. Dissociation between mean glucose metabolism rate and mean glucose metabolism rate-to-plasma insulin concentration ratio (M:I) was evident in the intensified training group during steady state of HEC testing after phases 3 and 4. After phase 4, mean glucose metabolism rate was significantly decreased (from 31.1 ± 6.8 μmol/kg/min to 18.1 ± 3.4 μmol/kg/min), as was M:I (from 1.05 ± 0.31 to 0.62 ± 0.17) during steady state in the intensified training group, compared with phase 3 values for the same horses.
Conclusions and Clinical Relevance—Dissociation between the glucose metabolism rate and M:I in horses that underwent intensified training may reflect non-insulin–dependent increases in glucose metabolism.
Objective—To investigate whether protein kinase C (PKC) isoforms are expressed in equine skeletal muscle and determine their distribution in various types of fibers by use of immunofluorescence microscopy.
Animals—5 healthy adult Dutch Warmblood horses.
Procedure—In each horse, 2 biopsy specimens were obtained from the vastus lateralis muscle. Cryosections of equine muscle were stained with PKC isoform (α, β1, β2, δ, ξ, or ζ)-specific polyclonal antibodies and examined by use of a fluorescence microscope. Homogenized muscle samples were evaluated via western blot analysis.
Results—The PKC α, β1, β2, δ, ξ, and ζ isoforms were localized within the fibers of equine skeletal muscle. In addition, PKC α and β2 were detected near or in the plasma membrane of muscle cells. For some PKC isoforms, distribution was specific for fiber type. Staining of cell membranes for PKC α was observed predominantly in fibers that reacted positively with myosin heavy chain (MHC)-IIa; PKC δ and ξ staining were more pronounced in MHC-I-positive fibers. In contrast, MHC-I negative fibers contained more PKC ζ than MHC-I-positive fibers. Distribution of PKC β1 was equal among the different fiber types.
Conclusions and Clinical Relevance—Results indicated that PKC isoforms are expressed in equine skeletal muscle in a fiber type-specific manner. Therefore, the involvement of PKC isoforms in signal transduction in equine skeletal muscle might be dependent on fiber type. ( Am J Vet Res 2004; 65:69–73)