Changes in serum muscle enzyme levels associated with training schedules and stage of the oestrous cycle in Thoroughbred racehorses.

Blood samples were collected twice weekly over a nine month period from 24 Thoroughbred racehorses in training at Newmarket to study the effects of daily training schedules and stage of oestrous cycle on serum enzyme levels and clinical signs of equine exertional myopathy. The sampling period extended from November to July and was performed between 16:00 h and 18:00 h so as to be at least 6 h after exercise. Serum creatine kinase, aspartate aminotransferase and plasma progestogen concentrations were measured. All horses were subjected to a similar traditional training programme. The study demonstrated marked fluctuations in serum muscle enzyme concentrations which were more pronounced in two-year-old fillies than three-year-old fillies and colts. There was no correlation, however, with the stage of oestrous cycle. It was concluded that some degree of muscle cell damage, which results in a variable increase in serum creatine kinase levels, occurs in all horses following light exercise after a rest day. Traditional flat race training may not be ideal in this respect and it is suggested that, for horses with an observed tendency towards exertional myopathy, more consistent and longer periods of less strenuous exercise may be advantageous.

Effects of dexamethasone on endotoxin shock in the anesthetized pony: hematologic, blood gas, and coagulation changes.

The effects of dexamethasone (1 mg/kg of body weight) on hematologic, blood gas, and blood coagulation values in anesthetized ponies during endotoxin-induced shock were evaluated. Fifteen ponies were assigned to 3 groups of 5 ponies each: group 1, anesthetized nontreated and dexamethasone-treated controls; group 2, endotoxin, nontreated; group 3, endotoxin, dexamethasone treated. The hematologic changes in this endotoxin shock model included leukopenia and hemoconcentration. Significant hematologic effects were not seen in ponies after administration of dexamethasone. However, dexamethasone treatment resulted in an increased trend in total WBC counts and neutrophils. The blood gas changes reflected a respiratory component resulting from anesthesia and a greater metabolic component from the endotoxemia. The plasma lactate increase was significantly (P less than 0.05) less in ponies treated with dexamethasone, compared with plasma lactate in non-treated ponies. During endotoxin shock, the changes observed in the blood coagulation values included a significant (P less than 0.05) prolongation of the activated partial thromboplastin time and thrombin time and an insignificant prolongation of the prothrombin time. Dexamethasone treatment prevented prolongation of thrombin time and permitted only a mild prolongation of activated partial thromboplastin time. Seemingly, corticosteroids are useful in the treatment of clinical endotoxin shock in horses as indicated by their desirable effects on total WBC, neutrophils, cellular metabolism, and blood coagulation.

Rn for treatment of periocular fibrous connective tissue sarcomas in the horse.

Twelve periocular fibrous connective tissue sarcomas in 11 horses were treated with 222Rn. Follow-up periods ranged from 1 to 6 years; the overall nonrecurrence rate at 12 months after therapy was 92%. Two lesions recurred 2 years after treatment, and 1 after 3 years. One of the former lesions has not recurred after a 2nd 222Rn treatment.

Endotoxin-induced change in hemograms, plasma enzymes, and blood chemical values in anesthetized ponies: effects of flunixin meglumine.

A study was made of flunixin meglumine (FM), an analgesic agent with antiprostaglandin activity, in the management of endotoxin-induced changes in ponies. Three groups of 5 ponies each were used: A--controls, B--nontreated ponies with endotoxin-induced shock, and C--ponies with endotoxin-induced shock treated with FM. Shock was induced in anesthetized ponies with IV injections of Escherichia coli endotoxin. Disruption of glucose homeostasis, insulin levels, hemograms, aerobic metabolism, and cell damage as indicated by plasma enzymes were observed. Treatment with FM (5 minutes) after shock was induced did not prevent general tissue damage as indicated by plasma enzymes, but separation of creatine phosphokinase into its 3 isoenzymes revealed a significant increase in the amount of the creatine phosphokinase isoenzyme bb in group B ponies, but not in FM-treated ponies (group C). The source of this isoenzyme is believed to be brain tissue. Acidosis as indicated by lactic acid and venous pH was less in FM-treated ponies than in nontreated (group B) ponies. Blood glucose and insulin concentrations changed in both groups B and C (endotoxin-induced shock), but the patterns of change were different. The only effect of FM on hematologic values was a significant decrease in blood platelet counts. The results of these experiments indicate that FM improved cellular metabolism and reduced brain damage. These effects were believed to be the result of the maintenance of mean arterial blood pressure and enhanced perfusion of vital organs by preventing extensive vasodilation in the gastrointestinal tract.

External cardiovascular resuscitation of the anesthetized pony.

External cardiac massage and concomitant respiratory support were used successfully 6 of 8 anesthetized ponies sustaining unexpected cardiac arrest while being used in a study of shock. Approximately 20 thoracic compressions/min maintained systolic and diastolic aortic blood pressures in excess of 50% of the corresponding base-line values in 5 ponies. The high success rate was attributed to early recognition of the problem, the small size of the patient, and the relatively short duration of cardiopulmonary resuscitation (average, 2.9 minutes). It was concluded that external cardiac message can be effective for cardiopulmonary resuscitation in selected equine patients that have sustained cardiac arrest.

Endotoxin-induced hemodynamic changes in ponies: effects of flunixin meglumine.

A study was made of flunixin meglumine, an analgesic agent with antiinflammatory and antiprostaglandin activity, for the management of endotoxin-induced cardiovascular derangements. Three groups of 5 ponies each were used: controls--group 1; given endotoxin but not treated--group 2; and given endotoxin and treated with flunixin meglumine--group 3. Shock was induced in anesthetized ponies with IV injection of Escherichia coli endotoxin. Hemodynamic changes were monitored, and regional blood flow was determined at 4 different times, using microspheres labeled with 1 of 4 nuclides. There were extensive vasodilation and decreased blood return to the heart of group 2 ponies, as indicated by decreased mean arterial blood pressure and central venous pressure and by increased heart rate and cardiac output. Blood flow, as determined by radioactive microspheres, to gastrointestinal regions, skeletal muscle, and skin was increased and that to the CNS was decreased. Treatment with flunixin meglumine (group 3 ponies) exerted selective microvascular actions which helped to reverse endotoxin-induced changes. This included the maintenance of mean arterial blood pressure and the enhanced perfusion of vital organs (eg, brain and heart) by preventing extensive vasodilation in the gastrointestinal tract.