Originally passed in 1958, the law was amended in 1978, then again in 2002. It requires USDA inspected slaughterhouses maintain the proper handling and humane treatment of all animals slaughtered excluding chickens. Specifically, animals must be unconscious before being slaughtered.  

Senator Hubert H. Humphrey was the original author of the bill but it was only signed into law after public outcry for humanely slaughtered animals and healthy facilities by President Dwight Eisenhower. The first version of the act required those selling meat to the U.S. government provide anesthetization or instant stunning by mechanical or electrical means prior to the killing of cattle, calves, horses, mules, sheep, swine and other livestock, except in the case of kosher slaughter. The measure covers 80% of livestock animals.

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