Whether bred to resist African Swine Flu (ASF), or with double muscles, Pigs are now on the forefront of genetic modification. The ASF-resistant pigs are still several years from being on our plates. They get their resistance from a gene from a African warthog (which is naturally resistant to the disease). Double-muscled pigs have leaner meat and a higher yield of meat per animal. However, they also have problems. Birthing difficulties result from the piglets’ large size, for instance.