The 168 pigs in the study were fed a diet of either GM or non-GM corn and soy over the course of their normal commercial lifespan (just over five months) at a pig farm in the United States. They were then autopsied by veterinarians after slaughter and tested for any significant differences across a wide range of measures.
The study found evidence that stomach inflammation classified as 'severe' was higher in pigs fed the GM diet. It also found that pigs in the GM feed group had, on average, a heavier uterus. There were no other significant differences between the disease status or weight of the organs of pigs in the two groups.
The results showed no significant differences in blood biochemistry, weight, illness, veterinary interventions or mortality between the two groups.
The full study is available here.