Effect of equine ehrlichial colitis on the hemostatic system in ponies

Hemostatic function was determined in 10 ponies at various times after inoculation with Ehrlichia risticii to determine whether equine ehrlichial colitis (EEC) caused changes in the hemostatic system and to determine the prognostic value of hemostatic function tests during EEC. Mean platelet count; plasma fibrinogen, fibronectin, factor VIII: coagulant, alpha 2-antiplasmin, and plasminogen values; and serum concentrations of fibrin/fibrinogen degradation products changed significantly (P less than 0.05) from base line (day 0, before inoculation) during 18 days after inoculation with E risticii. Four ponies that died or were euthanatized because of severe clinical signs of EEC had significantly (P less than 0.05) greater mean plasma fibrinogen concentrations plasma factor VIII:coagulant values, and activated partial thromboplastin times immediately before death than did the 6 surviving ponies. Factor V concentrations were significantly (P less than 0.05) lower on postinoculation days 10 and 20 in nonsurvivors. Seemingly, changes in hemostasis took place during EEC. Ponies that did not survive EEC had greater laboratory evidence of coagulopathy.     

Pathogenicity of equine herpesvirus 1 subtype 2 for foals and adult pony mares

Three pony mares and 4 pony foals were inoculated with a subtype 2 strain of equine herpesvirus 1. Foals had periods of fever 12 h and 2.5 days after inoculation and leukopenia, involving both neutrophils and lymphocytes, followed by leukocytosis. Mares had transient fever and leukopenia 24 hours after inoculation that were less severe than in foals. An increase in circulating virus-neutralizing antibody was seen in 2 of 3 inoculated mares, but not in foals. Attempts to isolate virus from blood were unsuccessful. These studies show that equine herpesvirus 1 subtype 2 is a mild pathogen for ponies and infection may result in inapparent clinical disease.     

Quantitative buffy coat analysis for hematologic measurements of canine, feline, and equine blood samples and for detection of microfilaremia in dogs

A quantitative buffy coat (QBC) analysis was evaluated for 175 canine, 125 feline, and 125 equine blood samples. The method used centrifuged whole blood and yielded rapid results expressed as respective band lengths for RBC, granulocytes, nongranulocytes, and platelets. Simple regression analysis of band lengths and reference laboratory methods yielded correlation coefficients (r) ranging from 0.72 to 0.99. The PCV, granulocyte count, and total WBC count, as determined by the 2 methods, correlated well (r greater than or equal to 0.93 in all cases). Platelet and nongranulocyte counts were less well correlated. The QBC system provided a means of performing rapid hematologic screening. The principal problem encountered was poor separation of the RBC-granulocyte interface in 17% of canine samples, which interfered with measurement of band lengths. Evaluation of the QBC tube for detection of Dirofilaria immitis microfilaremia revealed 100% sensitivity to counts as low as 160 microfilariae/ml of whole blood.     

Disease features in horses with induced equine monocytic ehrlichiosis (Potomac horse fever)

Fifty-five horses were inoculated IV and/or SC with materials containing Ehrlichia risticii, ie, infected whole blood, buffy coat cells, or cell culture, to study clinical and hematologic features of equine monocytic ehrlichiosis (Potomac horse fever). Major clinical and hematologic features of induced E risticii infection were biphasic increase in rectal temperature with peak increases of 38.9 C and 39.3 C on postinoculation days (PID) 5 and 12, respectively; depression; anorexia; decreased WBC count (maximal decrease of 47% on PID 12); and diarrhea from PID 14 to PID 18. Increased WBC count was an inconsistent feature, with a maximal increase of 51.5% on PID 20. During times of decreased and increased WBC counts, lymphocyte/neutrophil ratios remained fairly constant. However, not all horses had all clinical and hematologic features, and these features were present in different degrees among horses. Increased rectal temperature, depression, anorexia, and decreased WBC count were more consistent features, whereas diarrhea developed in 73% of the horses. Of 55 horses, 39 (71%) had all clinical and hematologic features of the disease (classic disease), whereas 16 (29%) horses did not have greater than or equal to 1 of these features (nonclassic disease). The E risticii titer in the blood (ehrlichemia) was maximum during the peak increase in rectal temperature. In 55 horses, mortality was 9%. Significant differences (P greater than 0.5) in clinical and hematologic features were not detected between horses that survived and those that died of E risticii infection.     

Functional and ultrastructural changes in neutrophils from mares and foals experimentally inoculated with a respiratory tract strain of equine herpesvirus-1

Neutrophils isolated from venous blood of adult and foal ponies inoculated with equine herpesvirus-1 were evaluated by in vitro function tests and by electron microscopy. Foals had fever and severe neutropenia 24 hours after inoculation; increased neutrophil random migration under agarose and decreased antibody-dependent cell-mediated cytotoxicity were significant at 24 hours, but values had returned to preinoculation levels by 72 hours. Mares had fever and leukopenia of less severity, increases in neutrophil migration, and longer persistence of primary granule release than were seen in foals. Reduced migration and degranulation, and a decrease in antibody-dependent cell-mediated cytotoxicity seen with neutrophils from foals, as compared with mares, may relate to the high susceptibility of foals to equine herpesvirus-1 infection.     

Hematology of the sandbar shark, Carcharhinus plumbeus: standardization of complete blood count techniques for elasmobranchs

BACKGROUND: Standardized hematologic methods and reference intervals have not been established for cartilaginous fishes (sharks, skates, and rays) despite the large number of animals displayed in zoos and aquariums worldwide. OBJECTIVE: The focus of this study was to validate CBC methods for sandbar shark (Carcharhinus plumbeus) blood, based on criteria established in human medicine, for the following tests: RBC count, total WBC count, PCV, hemoglobin (Hgb) concentration, and WBC differential percentages. METHODS: Replicate CBCs were performed using blood samples from 5 captive sandbar sharks. Three protocols for RBC and total WBC counts were compared, as were different centrifugation times for PCV determination, and 2 methods for Hgb concentration. Means, minimum and maximum values, and CVs were compared to CAP and CLIA performance guidelines for human tests. RESULTS: Total WBC counts in a diluent modified for elasmobranch blood, Hgb concentration by the cyanmethemoglobin method after removal of nuclei, and WBC differential percentages showed acceptable performance. PCV results were acceptable when tubes were centrifuged for at least 5 minutes. Total RBC counts by all 3 methods exceeded the acceptable error for manual counts of human cells. CONCLUSIONS: Standardized CBC tests can be used as health assessment tools for elasmobranchs. Total RBC counts should be viewed as estimates.     

Effects of aflatoxins in young ponies

Sixteen clinically normal, healthy ponies were randomly assigned to 4 groups and given aflatoxin B1 in doses of 0.045, 0.030, 0.015, and 0 (control) mg/kg of body weight per day for 21 days (or total doses of 0.945, 0.630, 0.315, and 0 mg/kg). The animals were allowed to recover for 3 months and then were reassigned to 4 treatment groups such that each group during the 2nd trial included a pony from each of the groups of the 1st trial. The animals in the new groups were intubated and were given aflatoxin in doses of 0.4, 0.2, 0.1, and 0 (control) mg/kg/day for 5 days ( or total doses of 2.0, 1.0, 0.5, and 0 mg/kg). Venous blood samples were drawn every other day to monitor for toxicosis; examinations were made for RBC and WBC counts, hemoglobin concentration, PCV, serum urea nitrogen, prothrombin time, and serum concentrations of aspartate aminotransferase, iditol dehydrogenase, alkaline phosphatase, albumin, gamma-glutamyl transferase, and arginase. There were no significant differences between treatment groups and controls (given no aflatoxin) in the toxicologic values examined for during the 1st trial. During the 2nd experiment, 2 of the ponies in the large-dose treatment gorup (2.0 mg/kg) demonstrated increased serum enzyme activities. These animals had been in the large-dose (0.945 mg/kg) and median-dose (0.63 mg/kg) groups during the 1st trial. Arginase, iditol dehydrogenase, and gamma-glutamyl transpeptidase activities became increased on the 4th day of treatment and continued to increase until the 6th day of the experiment (1 day after treatment was terminated). These enzymes approached control group values at 10 days after cessation of treatment. These increases were indicative of hepatocellular toxicity. It was concluded that the possibility of equine aflatoxicosis exists although ponies given high quality rations appear to be less susceptible than some other species. Prior exposure to aflatoxins may predispose to clinical toxicity on subsequent exposure, despite lack of expression of clinical signs.     

Analysis of feline,canine and equine hemograms using the QBC VetAutoread

Blood samples form 120 consecutive clinical cases (40 cats, 40 dogs and 40 horses) were analyzed on the QBC VetAutoread analyzer and the results compared with those obtained by a Baker 9000 electronic resistance cell counter and a 100-cell manual differential leukocyte (WBC) count. Packed cell volume (PCV), hemoglobin (Hb) concentration, mean cell hemoglobin concentration (MCHC), and platelet, total WBC, granulocytes, and lymphocyte plus monocyte (L+M) counts were determined. Indistinct separation of red blood cell and granulocytes layers on the QBC VetAutoread was observed in samples from five cats (12.5%), two dogs (5%), and one horse. Significantly different (P=0.002) median values for the two methods were obtained for PCV, Hb concentration, MCHC and platelet count in cats; PCV, MCHC, WBC, count and granulocytes count in dogs; and PCV, Hb concentration, MCHC and WBC, granulocytes and platelet counts in horses. Results from the QBC VetAutoread should not be interpreted using reference ranges established using other equipment. Results were abnormal on a limited number of samples; however, when correlation coefficients were low, marked discrepancy existed between values within as well as outside of reference ranges. Spearman rank correlation coefficients were excellent (r=0.93) for PCV and Hb concentration in dogs, and Hb concentration and WBC count in horses. Correlation was good (r=0.80-0.92) for PCV and Hb concentration in cats, WBC count in dogs, and PCV, granulocytes count and platelet count in horses. For remaining parameters, correlation was fair to poor (r=0.79). Acceptable correlations (r>0.80) were achieved between the two test systems for all equine values except MCHC and L+M count, but only for PCV and HB concentration in feline and canine blood samples.     

Effect of splenectomy on exercise-induced pulmonary and systemic hypertension in ponies

Large increases in systemic and pulmonary arterial pressures of exercising healthy ponies have been observed. Because exercise causes a considerable increase in PCV of ponies, we examined the effect of splenectomy on exercise-induced changes in systemic and pulmonary pressures. These pressures (taken with catheter-tip micromanometers) and indicator dilution cardiac output were determined on 9 healthy ponies that had undergone splenectomy 4 to 9 weeks before the study. Data obtained at rest and during submaximal (10.5 to 11.0 mph) and maximal (14 to 15 mph) exercise from these ponies were compared with similar data from clinically normal ponies. Following splenectomy, PCV increased by only 4 vol% during maximal exercise, but cardiac output of splenectomized ponies reached values similar to those of clinically normal ponies. Despite this similarity in cardiac output, the systemic and pulmonary arterial pressures of exercising splenectomized ponies increased to significantly lower levels than those in clinically normal ponies (P less than 0.01); total pulmonary vascular resistance and total peripheral resistance decreased to values significantly less than those in clinically normal ponies (P less than 0.01). Thus, it appears that increases in blood viscosity induced by increases in PCV may contribute substantially to the pulmonary and systemic hypertension of exercise in clinically normal ponies.     

Acute hemolytic anemia induced by oral administration of indole in ponies

Eight ponies were allotted to 2 groups of 4. Group-1 ponies (1-4) were given 0.2 g of indole/kg of body weight orally and group-2 ponies (5 to 8) were given 0.1 g of indole/kg. Various physical, hematologic, and physiologic measurements were obtained after administration of indole. Intravascular hemolysis and hemoglobinuria were detected in both groups within 24 hours of dosing. Hemolysis was reflected by decreases in PCV, hemoglobin concentration, and RBC count, and an increase in indirect bilirubin. Erythrocyte fragility appeared to increase in both groups at 8 hours after dosing and peaked at 16 hours after dosing. At 72 hours after dosing, the RBC fragility value was less than predose measurements. Heinz body formation was noticed in group-2 ponies, but not in group 1. Plasma indole concentrations increased in both groups from the nondetectable predose concentrations. Group-1 values were 203% of group-2 values. In group 2, plasma indole was nondetectable by 12 hours, whereas low concentrations could still be measured in the group-1 ponies at 24 hours. Ponies in group 1 died or were euthanatized between 24 and 72 hours after dosing, whereas group-2 ponies were euthanatized between 48 and 120 hours. At necropsy, all body fat, mucous membranes, and elastic tissue were stained yellow. Hemoglobinuric nephrosis was the most prominent microscopic lesion. Results of this study indicated that indole, a metabolite of the amino acid tryptophan, causes acute intravascular hemolysis in ponies.     

Effects of Castration on Peritoneal Fluid in the Horse

Twenty-four clinically normal horses were castrated by routine methods. Peritoneal fluid was collected prior to castration and at 1, 3, 5, and 7 days postcastration. Peritoneal fluid was collected on days 9 and 11 if nucleated cell (NC) counts were still markedly elevated on day 7. Peritonitis, defined as NC counts greater than 10,000/microliters, was evident in 15 horses following castration. Mean NC counts peaked on day 5 but were less than 10,000/microliters for 74% of the horses by day 7, and 90% of the horses by day 9. One horse had a NC count greater than 60,000/microliters on day 11 when sampling ended. Postcastration peritoneal fluid was obviously blood-tinged in 21 horses. Peak RBC counts occurred on day 3 but markedly decreased by day 5. Elevated peritoneal RBC counts correlated well with elevated NC counts (P less than 0.001). Horses with peritonitis tended to have fever (P less than 0.05). Other clinical signs of peritonitis were not apparent.     

Using red blood cell creatine concentration to evaluate the equine erythropoietic response

Red blood cell creatine concentration was examined to determine its association with the equine erythropoietic response. Studies were conducted on 9 healthy horses, 4 healthy ponies, 24 anemia horses, and 2 horses in which anemia was experimentally induced. A modified Jaffe reaction was used to measure RBC creatine concentration. The mean RBC creatine concentration of the 9 healthy horses was 5.72 +/- 0.42 mg/dl, and that of the 4 healthy ponies was 2.59 +/- 0.31 mg/dl. Density-separation of erythrocytes from the healthy horses revealed significantly higher (P less than 0.001) creatine content (7.72 +/- 0.57 mg/dl) in the young RBC populations than in the old RBC populations (4.03 +/- 0.27 mg/dl). The RBC creatine content was assayed in 19 hot-blooded horses which were anemic due to a variety of causes. Of these anemic horses, 12 with PCV between 25% and 30% had a mean RBC creatine concentration of 6.12 +/- 0.46 mg/dl. The 7 other anemic horses with PCV less than 25% had a mean RBC creatine value of 6.07 +/- 0.12 mg/dl. Bone marrow films were examined from 5 anemic horses and in the 2 horses in which anemia was experimentally induced. The RBC creatine concentration correlated positively (P less than 0.001) with the reticulocyte count in the bone marrow and negatively with the myeloid-erythroid ratio (P less than 0.001).     

Endotoxin-induced hematologic and blood chemical changes in ponies: effects of flunixin meglumine, dexamethasone, and prednisolone

To evaluate the effect of certain drugs on hematologic changes, blood chemical values, and survival in endotoxin shock, anesthetized ponies were given (IV) endotoxin (Escherichia coli O55:B5) and then treated as follows: Group A ponies--given a saline infusion at 5 minutes and at 3 hours after they were given endotoxin; group B ponies--given flunixin meglumine at 5 minutes and at 3, 6, 9, and 24 hours after they were given endotoxin; group C ponies--treated with dexamethasone; and group D ponies--treated with prednisolone at 5 minutes and at 3, 9, and 24 hours after they were given endotoxin. Anesthesia was maintained for 4 hours, after which time the ponies were allowed to recover. Throughout the experiment, samples of blood were collected for blood gas, hematologic, and blood chemical values. The endotoxin effects were seen in the 4 groups: lactic acidosis, prolonged coagulation times, leukopenia, hemoconcentration, and elevated blood chemical values. Although none of the treatments prevented the effects of endotoxin, changes were less severe and survival times were longer in ponies treated with flunixin meglumine.     

Hematologic and serum biochemical effects of long-term administration of anti-inflammatory doses of prednisone in dogs.

Results of routine hematologic and serum biochemical analyses from 12 healthy adult male dogs that were given prednisone (0.55 mg/kg of body weight, PO, q 12 h) for 35 days were compared with those of a control group of 6 dogs that were given gelatin capsules. Analyses were performed at 2-week intervals during and after prednisone administration. Lymphocyte and eosinophil counts were significantly (P less than 0.005) decreased after 2 and 4 weeks of prednisone treatment, compared with controls. Two weeks after treatment, eosinophil counts in prednisone-treated dogs were similar to those of control dogs, whereas lymphocyte counts remained low 4 weeks after treatment in treated dogs (1,869 +/- 145 cells/microliters), compared with that in control dogs (3,662 +/- 548 cells/microliters). Neutrophil and monocyte counts did not significantly change during glucocorticoid administration. Mean platelet volume significantly (P less than 0.001) decreased after 4 weeks of prednisone treatment, but returned to pretreatment values by 2 weeks after treatment. Four weeks of prednisone treatment did not cause significant increased activity in serum alanine transaminase, total alkaline phosphatase or the steroid-induced isoenzyme of alkaline phosphatase. Significant increases in serum albumin (P less than 0.001) and total protein (P less than 0.05) concentrations were detected after 4 weeks of treatment, but mean values were not significantly different from those of controls 2 weeks after treatment ended. Results of our study indicate that eosinophil and lymphocyte counts are the most sensitive indicators of long-term glucocorticoid administration at anti-inflammatory dosages of 1.1 mg/kg daily.     

Evaluation of equine hemograms using the ADVIA 120 as compared with an impedance counter and manual differential count

BACKGROUND: The ADVIA 120 is an automated laser cell counter widely used in veterinary medicine. Although specific software for equine samples is available and validated, only a few reports have been published comparing the ADVIA 120 with other methods for equine hemogram evaluation. OBJECTIVES: The purpose of this study was to compare the hematologic values and reference intervals obtained on the ADVIA 120 with those obtained on an impedance cell counter and manual differential counts in healthy horses. METHODS: EDTA-anticoagulated blood samples were obtained from 114 clinically healthy horses of various breeds, both sexes, and 2-6 years of age. Samples were stored for up to 12 hours at 4 degrees C and then analyzed on the ADVIA 120 and the Hemat 8. A 100-cell to 200-cell differential leukocyte count was performed by 3 independent observers on May-Grünwald-Giemsa-stained smears. Intra-assay precision of the ADVIA 120 was determined by analyzing 5 replicates each of 10 of the blood samples. RESULTS: Results from the ADVIA were significantly higher than those from the impedance counter for RBC count, total WBC count, hemoglobin concentration, red cell distribution width, MCH, and MCHC, and significantly lower for HCT and platelet count. Significantly higher neutrophil and basophil counts and significantly lower lymphocyte counts were obtained with the ADVIA 120 compared with manual counts. Based on Passing-Bablok regression analysis, RBC and platelet counts were in good agreement between the 2 analyzers; a constant and proportional bias was present for other values. Coefficients of variation for erythrocyte parameters on the ADVIA were <1%, but were higher for platelet (6%), total WBC (2%), differential WBC (4%-30%), and reticulocyte (75%) counts. CONCLUSIONS: Results obtained with equine samples on the ADVIA 120 were comparable with those obtained on an impedance counter; reference intervals differed statistically but overlapped. The ADVIA had poor precision for reticulocyte and differential leukocyte counts such that the latter should always be verified on smears.     

Immunity to equine herpesvirus type 1 (rhinopneumonitis): in vitro lymphocyte response.

Twenty-two ponies were examined for serum-neutralizing (SN) antibody to equine herpesvirus type 1 and for in vitro lymphocyte transformation in the presence of viral antigen. Six ponies had undetectable levels of neutralizing antibody (titer less than 1:2) and had lymphocytes which did not respond in culture with viral antigen (stimulation index less than 2.0). Four ponies which had SN antibody to equine herpesvirus type 1 did not manifest lymphocyte transformation in vitro. The 12 remaining seropositive ponies had lymphocyte transformation with viral antigen in vitro (stimulation indexes from 2.0 to 23.5). Lymphocyte transformation was specifically suppressed when cells were grown in medium containing autologous serum. The temporal development of in vitro lymphocyte responsiveness and SN antibody in 3 specific-pathogenfree ponies after experimentally induced infection with equine herpesvirus type 1 is described.     

Field performance of the equine parasiticide ivermectin in an oral paste

Ivermectin, a derivative of one of the avermectin compounds, was administered at 200 mcg per kg of body weight in an oral paste formulation to 80 mixed-breed ponies of both sexes and various ages. Twenty similar ponies received oral paste vehicle. Anthelmintic activity was determined by comparing fecal egg counts taken before and 14 days after ivermectin treatment to the counts of fecal samples from vehicle-treated controls. Commonly used equine vaccines were administered at the time of treatment. Sixteen of the 20 vehicle-treated ponies had positive counts prior to treatment and 17 were positive 14 days after treatment; 66 of the 80 ivermectin-treated ponies had positive counts prior to treatment; all 80 ponies had zero counts 14 days after treatment. The eggs were identified as strongylid in all the positive ponies while three ponies also hadOxyuris equi eggs prior to treatment.No adverse reactions were attributable to ivermectin oral paste treatment or concurrent vaccine administration.     

Comparative study of hematologic and plasma biochemical variables in Eastern Atlantic juvenile and adult nesting loggerhead sea turtles (Caretta caretta)

Background: Plasma biochemical and hematologic variables are important in the management of endangered sea turtles, such as loggerheads. However, studies on blood biochemistry and hematology of loggerheads are limited, and different concentrations according to variable criteria have been reported. Objective: The purpose of this study was to establish and compare baseline plasma chemistry and hematology values in Eastern Atlantic juvenile and adult nesting loggerhead sea turtles (Caretta caretta). Methods: Blood samples were collected from 69 healthy juvenile loggerhead sea turtles after their rehabilitation in captivity, and from 34 adult nesting loggerheads after oviposition. Fresh blood was used for leukocyte differential count and PCV determination. Heparinized blood was used for RBC and WBC counts. Plasma biochemical concentrations were measured using an automated biochemical analyzer. For the comparative study, nonparametric statistical analysis was done using the Mann–Whitney U‐test. Results: Minimum, maximum, and median concentrations were obtained for 14 hematologic and 15 plasma chemistry variables. Statistically significant differences between juvenile and adult turtles were found for PCV; RBC, WBC, and leukocyte differential counts; total protein, albumin, globulins, calcium, triglycerides, glucose, total cholesterol and urea concentrations; and lactate dehydrogenase activity. Conclusions: Age, size, and reproductive status cause important variations in the hematologic and plasma biochemical results of loggerheads. The reference values obtained in this study may be used as a standard profile, useful for veterinary surgeons involved in sea turtle conservation.     

Survival versus nonsurvival determinants for neonatal harbor seals

Of 29 neonatal harbor seals that had been abandoned, separated from their mothers, or stranded in the wild, 22 succumbed during hospitalization at the California Marine Mammal Center in the spring of 1982. Compared with standard reported harbor seal pup measurements, 8 of the nonsurviving pups were premature (ie, creamy-white lanugo coat, early pupping season birthdate, and decreased body size [6 to 10 cm shorter and 2.3 to 4.5 kg less than normal]). The premature pups and the young pups (less than or equal to 10 days old) had at least two of the following findings: jaundice, emaciation, labored respiration, hyperbilirubinemia, hypoglobulinemia, or leukopenia. Most of the nonsurviving pups died within 96 hours after admission. Macroscopic and microscopic findings indicated that a high percentage of these pups had pulmonary congestion and edema (72.7%), alveolar squamous cells/debris (27.3%), and/or congenital cardiac anomalies (ie, patent ductus arteriosus [63.6%] and patent foramen ovale [45.4%]). Two older pups (greater than 10 days old) died from chronic bacterial infections, accompanied by adrenal cortical hyperplasia. The 7 surviving pups had adult spotted pelage, normal body weights (9 to 11 kg), normal globulin concentrations (3.0 to 5.1 g/dl), and normal WBC counts (7 to 9 X 10(3)/microliters) and did not have clinical signs of icterus or respiratory distress.     

Effects of flunixin meglumine on blood pressure and fluid compartment volume changes in ponies given endotoxin

A study was conducted to determine whether body fluids undergo a net shift from one compartment to another during endotoxin-induced shock in the pony, and whether flunixin meglumine alters these endotoxin-induced changes in the volumes of body fluid compartments. Total blood, RBC, and plasma volumes were determined, using 51Cr-labeled RBC and PCV that were corrected for trapped plasma. Total body water was measured by distribution of 3HOH. Arterial blood pressure was measured directly, using a blood pressure transducer. Treatment (flunixin meglumine, 1.1 mg/kg of body weight) was given to 6 of the 12 ponies 1 minute before an IV injection of Escherichia coli endotoxin (100 micrograms/kg of body weight, LD100). The PCV and RBC volume increased in both groups; however, the hemoconcentration was less in flunixin meglumine-treated ponies. In nontreated ponies, total blood volume and plasma volume decreased significantly during the first hour after endotoxin administration. In treated ponies, total blood volume did not vary significantly, and plasma volume decreased only slightly. In both groups, the increase in PCV was apparently due to splenic contraction, which increased the number of circulating RBC. Hemoconcentration was further increased in nontreated ponies by the loss of plasma into the interstitial space. Flunixin meglumine reduced plasma loss, minimized hemoconcentration, and maintained normal blood volume. Total body water remained constant in treated and nontreated ponies.