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.