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- Author or Editor: K. Gary Magdesian x
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Abstract
OBJECTIVE
To evaluate changes in electrolyte concentrations and hydration status that take place in endurance horses prior to the start of a competition and determine whether these changes would be associated with elimination.
ANIMALS
19 horses entered in the 2016 Tevis Cup 100-Miles (160 km) One-Day Western States Trail Ride.
PROCEDURES
Heparinized blood samples were collected at 5 time points: prior to transport to the ride (T0), during check-in the day before the ride (T1), 1 to 2 hours before the start of the ride (T2), at the 15-km mark (T3), and at the 55-km mark (T4). Packed cell volume and plasma sodium, potassium, chloride, urea nitrogen, glucose, bicarbonate, and total protein concentrations were determined and compared across time points and between finishers and nonfinishers.
RESULTS
Signif icant differences were detected among plasma sodium, potassium, and urea nitrogen concentrations measured prior to the start of the ride (ie, T0, T1, and T2). For all variables except chloride and bicarbonate concentrations, significant differences were detected between values obtained prior to the start of the ride and values obtained during the ride (ie, T3 and T4). Only bicarbonate concentration at the 15-km mark of the ride was significantly associated with finishing status.
CONCLUSIONS AND CLINICAL RELEVANCE
Results suggested that significant changes in plasma sodium, potassium, and urea nitrogen concentrations can occur in endurance horses during transport to a competition and when horses are stabled overnight before an event. Additionally, a lower bicarbonate concentration following a steep climb early during the ride was associated with subsequent elimination.
Abstract
Objective—To determine disposition kinetics of amikacin in neonatal foals administered high doses at extended intervals.
Animals—7 neonatal foals.
Procedure—Amikacin was administered (21 mg/kg, IV, q 24 h) for 10 days. On days 1, 5, and 10, serial plasma samples were obtained for measurement of amikacin concentrations and determination of pharmacokinetics.
Results—Mean ± SD peak plasma concentrations of amikacin extrapolated to time 0 were 103.1 ± 23.4, 102.9 ± 9.8, and 120.7 ± 17.9 µg/mL on days 1, 5, and 10, respectively. Plasma concentrations at 1 hour were 37.5 ± 6.7, 32.9 ± 2.6, and 30.6 ± 3.5 µg/mL; area under the curve (AUC) was 293.0 ± 61.0, 202.3 ± 40.4, and 180.9 ± 31.2 (µg · h)/mL; elimination half-life (t1/2β) was 5.33, 4.08, and 3.85 hours; and clearance was 1.3 ± 0.3, 1.8 ± 0.4, and 2.0 ± 0.3 mL/(min · kg), respectively. There were significant increases in clearance and decreases in t1/2β, AUC, mean residence time, and plasma concentrations of amikacin at 1, 4, 8, 12, and 24 hours as foals matured.
Conclusions and Clinical Relevance—Once-daily administration of high doses of amikacin to foals resulted in high peak plasma amikacin concentrations, high 1-hour peak concentrations, and large values for AUC, consistent with potentially enhanced bactericidal activity. Age-related findings suggested maturation of renal function during the first 10 days after birth, reflected in enhanced clearance of amikacin. High-dose, extended-interval dosing regimens of amikacin in neonatal foals appear rational, although clinical use remains to be confirmed. (Am J Vet Res 2004;65:473–479)
Abstract
Objective—To determine values for total body water (TBW), extracellular fluid volume (ECFV), intracellular fluid volume (ICFV), and plasma volume (PV) in healthy neonatal (< 24 hours old) foals and to create a multifrequency bioelectrical impedance analysis (MF-BIA) model for use in neonatal foals.
Animals—7 healthy neonatal foals.
Procedures—Deuterium oxide (0.4 g/kg, IV), sodium bromide (30 mg/kg, IV), and Evans blue dye (1 mg/kg, IV) were administered to each foal. Plasma samples were obtained following an equilibration period, and the TBW, ECFV, ICFV, and PV were calculated for each foal. An MF-BIA model was created by use of morphometric measurements from each foal.
Results—Mean ± SD values were obtained for TBW (0.744 ± 0.024 L/kg), ICFV (0.381 ± 0.018 L/kg), ECFV (0.363 ± 0.014 L/kg), and PV (0.096 ± 0.015 L/kg). The 95% limits of agreement between the MF-BIA and indicator dilution techniques were within ± 2 L for TBW and ECFV.
Conclusions and Clinical Relevance—Fluid volumes in neonatal foals were found to be substantially larger than fluid volumes in adult horses. Multifrequency bioelectrical impedance analysis may be a useful technique for predicting TBW, ICFV, and ECFV in neonatal foals.
Abstract
OBJECTIVE To compare results of point-of-care laboratory testing with standard veterinary clinical examination findings at a single time point during endurance competition to identify horses at risk for elimination.
ANIMALS 101 endurance horses participating in the 2013 Western States 160-km (100-mile) endurance ride.
PROCEDURES At the 58-km checkpoint, blood samples were collected from all horses. Samples were analyzed for pH, Pco 2, base excess, anion gap, PCV, and whole blood concentrations of sodium, potassium, chloride, total carbon dioxide, BUN, glucose, and bicarbonate. Corrected electrolyte and PCV values were calculated on the basis of plasma total protein concentration. Immediately following the blood sample collection, each horse underwent a clinical examination. In addition to standard examination variables, an adjusted heart rate was calculated on the basis of the variable interval between entry into the checkpoint and heart rate recording. A combination of stepwise logistic regression, classification and regression tree analysis, and generalized additive models was used to identify variables that were associated with overall elimination or each of 3 other elimination categories (metabolic elimination, lameness elimination, and elimination for other reasons).
RESULTS Corrected whole blood potassium concentration and adjusted heart rate were predictive for overall elimination. Breed, plasma total protein concentration, and attitude were predictive for elimination due to metabolic causes. Whole blood chloride concentration and corrected PCV were predictive for elimination due to lameness. Corrected PCV was predictive for elimination due to other causes.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that for horses in endurance competition, a combination of breed and clinical examination and laboratory variables provided the best prediction of overall elimination.
Abstract
Objective—To determine gene expression of selected molecular markers (tumor necrosis factor [TNF]-α, interleukin [IL]-1β, IL-6, IL-8, IL-10, procalcitonin [PCT], and transforming growth factor [TGF]-β) in the blood of healthy and sick foals.
Animals—28 sick foals without sepsis, 21 foals with sepsis, and 21 healthy foals.
Procedures—Total RNA was extracted from blood samples and converted into complementary DNA (cDNA). Gene expression was measured for the molecular markers by use of real-time PCR assay, and final quantitation was performed with the comparative threshold cycle method.
Results—Samples from all foals yielded transcription for all markers. Expression of TNF-α and TGF-β was significantly lower and that of IL-8 significantly greater in the sick-nonseptic and septic groups, compared with the healthy group. No significant difference in expression of IL-1β, IL-6, and PCT was found between the healthy group and the 2 sick groups. Expression of IL-10 was significantly greater in nonsurvivors, compared with survivors.
Conclusions and Clinical Relevance—The cytokine profile in foals with sepsis may suggest an immunosuppressive state. Expression of IL-10 may be a marker for identification of foals with a guarded prognosis.
Abstract
OBJECTIVE
To determine whether IV regional limb perfusion (IVRLP) performed in the cephalic vein with a wide rubber tourniquet (WRT) applied proximal and distal to the carpus results in a higher peak concentration (Cmax) of amikacin in the radiocarpal joint (RCJ), compared with the Cmax for IVRLP using a single WRT proximal to the carpus.
Animals
7 healthy adult horses.
Procedures
Horses underwent IVRLP using standing sedation with 2 g of amikacin sulfate diluted to 60 mL by use of saline (0.9% NaCl) solution in the cephalic vein with 2 different tourniquet techniques; proximal WRT (P) and proximal and distal WRT (PD). Synovial fluid was collected from the RCJ at 5, 10, 15, 20, 25, and 30 minutes after IVRLP. Tourniquets were removed after the 30-minute sample was collected. Blood samples from the jugular vein were collected at 5, 10, 15, 20, 25, 29, and 31 minutes after IVRLP. Amikacin concentration was quantified by a fluorescence polarization immunoassay. Median peak concentration (Cmax) of amikacin and time to maximum drug concentration (Tmax) within the RCJ were determined.
Results
Median peak concentration in the RCJ was 1331.4 μg/mL with technique P and 683.1 μg/mL with technique PD. Median Tmax occurred at 30 minutes with technique P and 25 minutes with technique PD. No significant (Cmax, P = 0.18; Tmax, P = 0.6) difference in amikacin Cmax or Tmax between techniques was detected.
Clinical Relevance
Placement of 2 WRTs offers no advantage to a single proximal WRT when performing IVRLP to deliver maximal amikacin concentrations to the RCJ using IVRLP.
Abstract
Objective—To determine whether high liver enzyme activities were negatively associated with outcome in sick neonatal foals as compared with foals that did not have high liver enzyme activities.
Design—Retrospective case-control study.
Animals—147 foals < 30 days old with high γ-glutamyltransferase activity, high sorbitol dehydrogenase activity, or both (case foals) and 263 foals < 30 days old with γ-glutamyltransferase and sorbitol dehydrogenase activities within reference limits (control foals).
Procedures—Medical records were reviewed for information on signalment, physical examination findings, and results of hematologic and serum biochemical analyses performed at the time of admission to a veterinary medical teaching hospital.
Results—Case foals were significantly more likely to die or be euthanized, compared with control foals (odds ratio, 2.22; 95% confidence interval, 1.28 to 3.85). Case foals were significantly more likely than control foals to have sepsis, and septic foals were significantly less likely to survive than were nonseptic foals. For case foals, other factors associated with a greater likelihood of nonsurvival were higher anion gap and higher logarithm of aspartate aminotransferase activity. When sepsis status was controlled for, the presence of high liver enzyme activities was not significantly associated with outcome.
Conclusions and Clinical Relevance—Results suggested that high liver enzyme activities were common in sick neonatal foals, especially foals with sepsis. Foals with high liver enzyme activities were more likely to be septic, and septic foals were less likely to survive than were foals without sepsis. However, high liver enzyme activities alone were not a useful negative prognostic indicator.
Abstract
Objective—To evaluate selected hemodynamic, blood gas, and biochemical responses to mild to moderate acute blood loss in standing, awake horses.
Design—Prospective study.
Animals—7 healthy mares.
Procedures—Each horse was restrained in standing stocks, and its head was maintained in a neutral position; sedatives and tranquilizers were not administered. During a 1-hour period, blood was collected into collection bags by use of a suction pump. The rate of blood collection was approximately 16 mL/kg/h (7.3 mL/lb/h). Thirty minutes after blood collection, the blood was readministered at the same rate. Central venous pressure (CVP), central venous blood gas, blood lactate concentration, and heart rate were measured at baseline (after placement of catheters), after removal of blood, and after readministration of blood.
Results—In response to blood loss, CVP decreased and blood lactate concentration increased significantly, compared with baseline values; heart rate and results of central venous blood gas analysis did not change significantly. After readministration of blood, CVP returned to baseline value and blood lactate concentration approached baseline value.
Conclusions and Clinical Relevance—Changes in CVP and blood lactate concentration appear to be early indicators of hypovolemia in horses, which may represent acute blood loss in trauma patients; these variables should be monitored to assess the potential need for blood transfusions. These variables can be used to monitor responses of horses to blood transfusions when whole blood is administered as the replacement fluid.
Abstract
Case Description—A 4-month-old American Paint filly was evaluated because of sudden onset of ataxia that progressed to recumbency. Five additional horses from the same and neighboring premises developed signs of poor performance, generalized weakness, ataxia, and recumbency; 2 of those horses were also evaluated. A new batch of a commercial feed supplement had been introduced to the horses' diet on each farm within the preceding 3 days.
Clinical Findings—Other than recumbency, findings of physical and neurologic examinations of the foal were unremarkable. The other 2 horses had generalized weakness and mild ataxia, and 1 horse also had persistent tachycardia. The foal had mild leukocytosis with neutrophilia, hyperglycemia, and mildly high serum creatine kinase activity. Results of cervical radiography, CSF analysis, and assessments of heavy metals and selenium concentrations in blood and vitamin E concentration in serum were within reference limits. Feed analysis revealed high concentrations of the ionophore antimicrobial salinomycin.
Treatment and Outcome—The 5 affected horses survived, but the foal was euthanized. At necropsy, a major histopathologic finding was severe vacuolation within neurons of the dorsal root ganglia, which was compatible with ionophore toxicosis. The surviving horses developed muscle atrophy, persistent weakness, and ataxia.
Clinical Relevance—In horses, ionophore toxicosis should be considered as a differential diagnosis for acute weakness, ataxia, recumbency, or sudden death. Furthermore, ionophore toxicosis should be considered as a cause of poor performance, weakness, muscle wasting, and cardiac arrhythmias in horses. Surviving horses may have impaired athletic performance.
Abstract
Objective—To compare clinical, microbiologic, and clinicopathologic findings among horses infected with Clostridium difficile that had toxin A in their feces, horses with evidence of C difficile infection that were negative for toxin A in their feces, and horses with diarrhea that were negative for C difficile infection.
Design—Cross-sectional study.
Animals—292 horses and foals with diarrhea.
Procedures—Feces were submitted for microbial culture and tested for the C difficile antigen glutamate dehydrogenase and for toxin A with a commercial ELISA.
Results—Horses with toxin A in their feces had higher band neutrophil count, rectal temperature, hospitalization time prior to the onset of diarrhea, and total hospitalization time than did horses without evidence of C difficile infection, and 32 of the 33 (97%) horses with toxin A in their feces had received antimicrobials prior to the onset of diarrhea. Horses with toxin A in their feces had a significantly higher mortality rate than did horses negative for toxin A in their feces. Sensitivity and specificity of the ELISA for detection of C difficile antigen were 93% and 88%, when assay results were compared with results of microbial culture following direct plating, and 66% and 93%, when assay results were compared with results of microbial culture following broth enrichment.
Conclusions and Clinical Relevance—Results provided some evidence that horses positive for toxin A had more severe clinical disease than did horses with evidence of C difficile infection that were negative for toxin A and horses with diarrhea without evidence of C difficile infection.
