Hereditary (genetic) and congenital diseases are quite common in swine and include a range of conditions. The term "hereditary" indicates that the condition was inherited by the piglet from the sow's or the boar's genes. The term "congenital" means that the condition is present at birth but implies it is a developmental abnormality that occurred during the growth of the foetus while in the uterus, rather than a hereditary defect or abnormality.

This said, some developmental abnormalities are not evident at birth, for example, an inguinal hernia, and these develop at a later stage - described as delayed developmental abnormalities. If a congenital defect occurs frequently and is related to a particular line or breed then it is likely to be hereditary.

Defects in the piglet can also arise form nutritional issues, poisoning, infectious agents or spontaneously due to abnormal metabolism.

Most hereditary or congenital defects remain at a low incidence because breeding programmes cull affected animals. However, occasionally a boar can be identified as being associated with a higher incidence of an abnormality than usual. A typical example would be umbilical hernia. (This condition can also be precipitated by abdominal pressure).

Another type of problem that occurs at birth is difficulty in farrowing associated with a small or abnormal development of the pelvis.

Embryo mortality varies considerably both between breeds and individuals, and heredity plays an important but as yet ill-defined part. In most herds, records show that congenital malformations range from 0.5 to 2.5 percent with an average of approximately 1.5 percent. However, if all the defects were recorded then levels would approach three percent. Common developmental defects are described in Fig.2-13, the causes of which are often multifactorial in origin.