Pathology and epidemiology of conjoined twinning in swine

Among 67 pigs with conjoined twinning observed over four and one‐half years the majority had partial rather than complete twinning. Fifty‐two percent of the 67 pigs were classified as syncephalus, i.e., with 1 head and two bodies. Epidemiologically, most were crossbred pigs born in February, March, and April on farms scattered throughout the swine‐producing regions of Missouri. In addition each was the only deformed pig in the litter. Comparison of some 32 swine husbandry variables for conjoined twin herds and matched‐paired environmental control herds did not identify any major environmental or genetic factors associated with conjoined twinning in Missouri swine.