Cardiomyopathy and woolly haircoat syndrome of Poll Hereford cattle: electrocardiographic findings in affected and unaffected calves.

Electrocardiograms were recorded from 4 calves with cardiomyopathy and woolly haircoat syndrome (CWH), a lethal autosomal recessive trait of Poll Hereford cattle and from 9 unaffected calves. Electrocardiograms of calves with CWH were characterised by multifocal ventricular premature contractions which occurred singly, in pairs, in runs and as episodes of ventricular tachycardia. Bigeminal rhythms were recorded occasionally. The frequency of ventricular premature contractions ranged from 5 to 120.min-1. Ventricular premature contractions in calves with CWH were attributed to myocardial degeneration and fibrosis which were observed grossly and microscopically. Electrocardiograms in unaffected calves were characterised by normal sinus rhythm and by variation in the morphology of wave forms between animals. The durations of the various wave forms were less than those previously recorded from adult cattle.