The following informations we got from wikipedia and several online websites.
Animal welfare in the USA
The Animal Welfare Act in the United States regulates the treatment of animals which are kept in research facilities or zoos at the national level. It's called the "Animal Welfare Act" (AWA) and has existed since August 24, 1966.
Unfortunately, there is no corresponding national law for the husbandry and treatments of livestock farming.[1]
Slaughtering
In the USA, there has been a law since 1958 that farm animals must be stunned before slaughter to minimize pain.
Hühner, Truthähne und Vögel sind jedoch nicht in diesem Gesetz enthalten. Weshalb diese Tiere anders empfinden als andere Nutztiere ist unklar. [2]
Transport
In the USA, livestock farming can be transported without food or water for 28 hours. Loading or unloading can increase the total time to 36 hours. This law has existed since 1873.