Morphometry of bovine dilated cardiomyopathy.

Bovine dilated cardiomyopathy (BDCM) is a primary disease of the myocardium that has been described in Holstein-Friesian cattle worldwide in the last 20 years. The principal morphological changes in the myocardium are interstitial fibrosis and increased variability in cardiomyocyte size. Sections of heart muscle from nine cases of BDCM and nine unaffected controls matched for age, sex and breed were studied by means of a computer-assisted image analyser to measure the degree of fibrosis, and the cardiomyocyte cellular and nuclear cross-sectional area and length. The amount of connective tissue in the hearts of BDCM cases was increased by 6.7 times, the nuclear transverse cross-sectional area by 1.9 times, and the cardiomyocyte length and cross-sectional area by 1.7 and 1.6 times, respectively. This resulted in an estimated 2.5-fold increase in mean cardiomyocyte volume. Animals with clinical signs of BDCM showed a mean loss of 51% of the total number of cardiomyocytes as compared with controls. Of the five parameters studied, the percentage of fibrosis was found to be the most consistent discriminator for BDCM. It is possible that the degree of fibrosis could be used to distinguish BDCM from other cardiac diseases of cattle.