The "beef trust" comprised a few large companies that controlled the Union Stockyards in Chicago. Upton Sinclair became a worker in the stockyards for the purpose of gathering information that he would later use in his book "The Jungle." Published in 1906, "The Jungle" exposed the unsanitary conditions under which impoverished workers toiled in the packing plants. From the publicity generated by the book, pressure was brought on Congress to conduct investigations, the ultimate result of which was the Meat Inspection Act.
As a companion measure to the Pure Food and Drug Act, the Meat Inspection Act brought the following reforms to the processing of cattle, sheep, horses, swine and goats destined for human consumption:
All animals were required to pass an inspection by the U.S. Food and Drug Administration prior to slaughter
All carcasses were subject to a post-mortem inspection
Cleanliness standards were established for slaughterhouses and processing plants.
The Beef Trust fought against passage of the Meat Inspection Act, but could not prevent its becoming law.