Congenital heart defects in cattle
Congenital heart defects (CHD) are cardiac diseases present at birth and a prevalence of 0.2% to 2.7% has been reported in cattle. However, the real prevalence of bovine CHD could be underestimated because of the scarcity of surveillance programs and the low economical value of young animals, this leads the farmers to limit further diagnostic tests in calves suspected to have CHD. Moreover, many calves can have asymptomatic CHD that go undetected or die during the perinatal period before veterinary examination. The precise cause of CHD is not known in cattle and external teratogens or genetic factors can be implicated in the genesis of CHD. The use of selected sires for intensive breeding programs, especially in some of breeds with low population size, has increased the “inbreeding grade” that could be responsible for CHD. Congenital cardiac defects can be classified by various criteria and, in relation to the presence of cyanosis of the mucous membranes, they can be subdivided into cyanogenic or non-cyanogenic CHD. Ventricular septal defects, atrial septal defects and persistent ductus arteriosus are the most frequently reported non-cyanogenic CHD in cattle. Complex CHD such as conotruncal anomalies (tetralogy of Fallot, complete transposition of the great arteries and double-outlet right ventricle) are commonly described as cyanogenic CHD. Rare CHD such as malformations of atrioventricular valves, outflow tract obstructions and anomalies of vessels connected to the heart are less frequently diagnosed in the bovine species. This review aims to provide a summary of the most common CHD reported in cattle with the iconographic support from the authors' experience, offering thus an overview of which congenital anomalies should be considered during the evaluation of cattle suspected to have CHD. A precise diagnosis can be useful in cases with isolated defects, which can be associated with a favorable prognosis; likewise, it can be important an accurate and early diagnosis in cases with severe and complex malformations, often associated with a poor prognosis for long-term productivity and survival. This is of primary importance in order to avoid unnecessary treatments or animal suffering.