A review of congenital malformations in swine relating to abnormal twinning was carried out. The aim was to describe and estimate these defects. Among the recorded twins, the most common defect was the syncephalus thoracopagus or cephalothoracopagus. A couple of dicephali and diprosopus congenital anomalies were also registered. At last, some cases of thoraco-omphalopagus piglets were surveyed. There was also a report of an acardiac twin (hemiacardius acephalus) and a case of a conjoined parasitic twin. The pathogenetic mechanisms of this condition, frequently reported in veterinary practice, are discussed. The importance of embryonic imperfect twinning is commonly associated with dystocia.
Keywords: congenital malformations; conjoined twins; pig; teratology.