Responding to a legal petition from animal-rights groups, USDA officials now say that a 133-year-old law regarding livestock transportation by train also applies to truck transport. Congressional changes made in 1994 make livestock moved by trucks subject to the federal "28-Hour Law." That law requires animals to be unloaded, fed, watered and rested after 28 consecutive hours of transportation.

The Humane Society of the United States, Farm Sanctuary, Compassion Over Killing and Animals' Angels filed the petition last October, claiming public-health concerns from animals kept on trucks longer than 28 hours. USDA dismissed those claims but said the “meaning of a vehicle” includes trucks.

While few pigs are transported far enough to be on a truck for 28 hours, the National Pork Producers Council is evaluating law’s impact on the industry. Biosecurity is a major concern, as disease transmission chances (including cross-species contamination) greatly increases if animals are off-loaded at common rest stations.