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Polioencephalomalacia, a disease of ruminants, is most likely due to a thiamine deficiency and is most frequently associated with intensive feeding conditions or with recent changes in management. The clinical signs of incoordination and blindness followed by recumbency and opisthotonus can resolve relatively rapidly when treated early with thiamine and supportive care. The disease can frequently be prevented by thiamine supplementation and inclusion of a minimum amount of roughage in feedlot rations.

Cardiac arrhythmias are common in horses and are frequently associated with complaints of exercise tolerance. Physical examination is utilized to classify the arrhythmia according to rate, regularity, pauses, added or abnormal sounds. The electrocardiogram is used to make a definitive diagnosis of the arrhythmia and to monitor the effects of treatment. Antiarrhythmic therapy is given when clinical signs specifically related to the arrhythmia are present, when hemodynamic parameters are compromised by the arrhythmia, or when the electrocardiogram reveals abnormalities that put the patient at risk for development of more severe arrhythmias. The drugs most commonly used are digoxin for treatment of supraventricular arrhythmias and arrhythmias with fast rates and quinidine for treatment of ventricular and supraventricular arrhythmias.

The rational therapy of cardiovascular disease in horses requires a thorough knowledge of the pharmacology and pharmacokinetics of several specific drugs (digitalis, digoxin). Calcium solutions, dopamine, and dobutamine are frequently used to treat congestive heart failure in horses. Quinidine, procainamide, lidocaine, and propranolol are used to treat a variety of supraventricular and ventricular arrhythmias. Furosemide, a highly potent loop diuretic, is used to eliminate edema and promote diuresis. A thorough understanding of the applied pharmacology, dosage recommendations, toxicity, and practical considerations must be attained before these drugs can be used effectively.