Cardiovascular causes of exercise intolerance.

Exercise intolerance, due to cardiovascular disease in horses, may be caused by cardiac arrhythmias, valvular regurgitation, congenital abnormalities, myocardial dysfunction, pericardial disease, and vascular thrombosis. The most common cardiovascular cause of exercise intolerance in horses is atrial fibrillation. Cardiovascular abnormalities such as cardiac arrhythmias or murmurs, however, are common in athletic horses and are not always associated with exercise intolerance. Use of an electrocardiography (during rest and exercise) and echocardiography may be necessary to better determine the significance of the cardiovascular abnormality.

Phenylbutazone increases right atrial pressure and heart rate of running horses.

The effect of inhibition of cyclooxygenase activity on the hemodynamic response to exertion was examined in 6 horses. Rates of O2 consumption and CO2 production and carotid, pulmonary arterial, and right atrial pressures were measured while the horses performed a standardized exercise test on a treadmill after treatment with phenylbutazone or a placebo. Phenylbutazone (8.8 mg/kg p.o. for 2 days and 4.4 mg/kg i.v. 60 min before exertion) abolished the exertion-induced increases in plasma 6-ketoprostaglandin F1 alpha and thromboxane B2 concentrations, confirming inhibition of cyclooxygenase activity. Phenylbutazone treatment resulted in significantly (P < 0.05) higher heart rates and right atrial pressures during exertion than did treatment with placebo, which may have been due to increased myocardial sensitivity to sympathetic stimulation and/or decreased venous compliance. There was not a detectable effect of phenylbutazone on carotid or pulmonary arterial pressures, O2 consumption, CO2 production, or blood lactate concentration. Changes in plasma volume during exertion were not influenced by phenylbutazone. These results demonstrate that cyclooxygenase products likely mediate or modulate some of the systemic hemodynamic responses to exertion in horses.

Necrotizing enterocolitis in horses: a retrospective study.

The clinical and clinicopathologic characteristics of fatal necrotizing enterocolitis were examined in 16 horses (age 4 months to 12 years). At initial presentation, 8 of 16 horses were pyrexic (median temperature, 38.4 degrees C; range, 33.8 to 40.6 degrees C); all 16 were tachycardic (median heart rate, 93 bpm, range, 66 to 138 bpm); 13 of 16 were tachypneic (median heart rate, 36 bpm, range, 16 to 80 bpm), dehydrated, and had discolored mucous membranes. All horses that were pyrexic were also tachycardic and tachypneic. PCV was high (> 45%) in 14 horses. Six horses were leukopenic (< 5,000 cells/microL); 12 were neutropenic (< 2,300 cells/microL), and 14 had > 100 band neutrophils/microL. Twelve horses were acidemic (pH < 7.37; range, 6.88 to 7.33) and the venous bicarbonate concentration was low (< 23 mEq/L) in 14 horses. Median anion gap in 16 horses was 31.5 mEq/L (> 15 mEq/L in 15 horses). Eleven of 16 horses were hyponatremic (< 137 mEq/L), 1 horse was hypernatremic (> 143 mEq/L), 3 were hypokalemic (< 3.2 mEq/L), 6 were hyperkalemic (> 4.5 mEq/L), and 14 were hypochloremic (< 98 mEq/L). Serum creatinine concentrations were high (> 1.4 mg/dL) in 15 horses. Abdominal fluid was examined in 12 horses 4 had total protein concentrations > 2.5 g/dL and 6 had nucleated cell counts > 5,000/ microL and < 10,000/microL; none had > 10,000/microL. Eight of 12 samples revealed a nondegenerate neutrophilia (> 50%). Abdominal fluid collected from 4 horses immediately before death was normal in 2 horses and indicative of suppurative inflammation in 2. All 8 horses tested had low or nonexistent serum immunofluorescent antibody titers to Ehrlichia risticii. Four of 16 horses had Salmonella spp isolated from feces or tissues. All 16 horses either died (5 of 16; 31%) or were euthanized because of a grave prognosis. Median time to death was 45.5 hours (range, 7 to 113 hours) from the time of admission. Death was preceded by severe abdominal pain in 14 horses. Fatal necrotizing enterocolitis of horses is characterized by a brief course, profound dehydration, electrolyte derangements, acid-base abnormalities, and terminally, severe abdominal pain. Abdominal fluid analysis was frequently not indicative of the severity of disease.

A portable blood gas analyzer for equine venous blood.

Evaluation of a portable blood gas analyzer, (StatPal II, Unifet, Inc, La Jolla, CA) was performed using tonometered solutions and equine blood. Samples were analyzed by the StatPal II and either an Instrument Laboratory IL1306 (Lexington, MA) or a Radiometer ABL50 blood gas analyzer (Radiometer America Inc., Westlake, OH). Comparison of the StatPal II and the IL1306 was done by analysis of 3 tonometered solutions (acidic, normal, and alkalotic) and 27 equine venous blood samples. Blood pH, PCO2, PO2, and [HCO3] values were altered by IV infusion of 5% sodium bicarbonate or exercising the horses on a treadmill. Comparison of the StatPal II and the Radiometer was performed by analysis of 78 blood samples collected from Standardbred horses before a race. Data were analyzed for the venous blood samples using a paired two-tailed Student's t test and Bland-Altman plots, with significance set at P < .05. The coefficients of variation for pH, Pco2, Po2, and [HCO3-] values of the tonometered solutions analyzed by the StatPal II ranged from 0.067% to 0.087%, 2% to 3.21%, 1.21% to 2.67%, and 0.267% to 0.828%, respectively. Comparison of the equine blood samples analyzed by the StatPal II and the IL1306 demonstrated statistically significant, but clinically irrelevant differences in pH, Pco2, and Po2, but not [HCO3-]. There were statistically significant, but clinically irrelevant differences between the StatPal II and the Radiometer for pH, Pco2, and [HCO3-], but not for Po2. It is concluded that the StatPal II provides reproducible and acceptable analysis of equine venous blood gas samples.

Racing performance after hemicircumferential periosteal transection for angular limb deformities in thoroughbreds: 199 cases (1987-1989).

Racing records of 199 Thoroughbred foals with angular limb deformities surgically treated by hemicircumferential periosteal transection and elevation (HCPT) from 1987 through 1989 (principals) were compared with records of their 1,017 siblings (controls) for starting status; 2-, 3-, and 4-year-old starts; earnings and earnings per start; and starts percentile ranking number (SPR). Principals had a slightly lower percentage of horses starting a race (45 vs 55%), fewer 2-year-old starts (1.06 vs 1.72), and lower SPR (33.49 vs 49.18), compared with those of controls (P < 0.05). Starting status was significantly (P < 0.05) affected by surgery and the horse's sex, but not by anatomic site treated. Fillies were 1.74 times less likely to start than were colts, regardless of surgery, whereas principal fillies were 2.63 times less likely to start than were control colts. Difference was not detected between principals and controls in 3- or 4-year-old starts; 2-, 3-, or 4-year-old earnings, or earnings per start. Horses treated with distal metacarpal/metatarsal HCPT had fewer 2-year-old starts (1.09 vs 2.19), but did not have a significantly different SPR or lower starting percentage, compared with values for controls. Horses treated with distal radial HCPT had lower starting percentage (48 vs 55%), fewer 2-year-old starts (1.22 vs 1.70), and lower SPR (32.53 vs 53.32), compared with those of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovariohysterectomy in six mares.

Six mares had ovariohysterectomy performed for chronic pyometra associated with cervical abnormalities, uterine neoplasia, or removal of a macerated fetus. Ovariohysterectomy was performed through a ventral midline incision with access to the ovarian and uterine vessels aided by traction on the uterus and retraction of abdominal viscera. Abdominal pain, the most common complication after surgery, occurred in four mares but resolved within 36 hours. Peritonitis occurred in two mares; one mare was subsequently euthanatized. Other complications that resolved with treatment included infection of the uterine stump (two mares), abdominal hemorrhage (one mare), diarrhea (one mare), and incisional infection (one mare). Complications after surgery can be reduced by removing as much of the uterus as possible, minimizing peritoneal contamination with uterine contents, and providing a secure closure of the caudal reproductive tract.

Effect of exercise intensity on plasma prostaglandin concentrations in horses.

Exertion has an effect on plasma, serum, and/or urine prostanoid concentrations in many species. We investigated the effect of exercise intensity on plasma prostaglandin concentrations during and after exercise in horses. Six Thoroughbreds completed 4 trials: 3 exercise trials (low-, medium-, and high-speed) and 1 nonexercise (control) trial on a high-speed treadmill. Blood samples were collected from a jugular catheter before, during, and after exercise. The PCV and blood lactate, plasma protein, plasma prostacyclin (6-keto-PGF1 alpha), thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) concentrations were measured before, during, and after exercise. Exercise significantly (P = 0.001) increased plasma TXB2 concentration during and after exercise in the low-, medium-, and high-speed trials, although effect of exercise intensity was not detected. Exercise was associated with an increase in PCV and blood lactate and plasma protein concentrations. There was no effect of exercise on plasma 6-keto-PGF1 alpha concentrations; PGE2 was not detected in plasma from any horse in any trial.

Furosemide, bumetanide, and ethacrynic acid.

Furosemide and, less commonly, bumetanide and ethacrynic acid are potent diuretics administered to horses for a variety of reasons, including prophylaxis of exercise-induced pulmonary hemorrhage. These drugs affect urine volume and composition, and furosemide has marked effects on plasma volume and composition and on systemic hemodynamics at rest and during exercise.

Diagnosis of EDTA-dependent pseudothrombocytopenia in a horse.

Thrombocytopenia in horses may be idiopathic or secondary to chronic infectious or inflammatory diseases (eg, equine infectious anemia, lymphosarcoma), drug administration, bone marrow depression, myelophthisic disease, or disseminated intravascular coagulation. This report describes EDTA-dependent pseudothrombocytopenia in a horse. Platelet counts for blood containing EDTA were consistently less than reference range, but platelet counts of blood containing heparin were within reference range. When thrombocytopenia is diagnosed in horses without clinical evidence of a bleeding tendency, EDTA-dependent pseudothrombocytopenia should be considered. The diagnosis can be confirmed simply by screening blood films for platelet clumps and by comparing platelet counts of paired blood samples, one containing EDTA and the other containing heparin.