Early veterinary studies seemed to support the use of gestation crates. According to the U.S. National Pork Producers Council, which promotes pork as a food product and is a leading proponent of gestation crates, the American Veterinary Medical Association "recognize gestation stalls and group housing systems as appropriate for providing for the well-being of sows during pregnancy." While the practice of immobilizing the animals in crates limits fighting, it subsequently increases the animals' stress levels, causing other health problems. The American Association of Swine Veterinarians adopted a position statement in 2002 specifying five standards of sow welfare and concluding, "Current scientific literature indicates that individual gestation stalls meet each of the aforementioned, provided the appropriate level of stockmanship is administered."