Final answer:
The rule livestock producers must follow is the Country of Origin Labeling (COOL) rule, which was implemented in October 2008 to ensure transparency in the meatpacking industry.
Step-by-step explanation:
Livestock producers must provide definitive origin information to slaughter facilities under the new Country of Origin Labeling (COOL) rule that went into effect in October 2008. In response to concerns about consumer safety and the transparency of the meatpacking industry, this rule was part of a series of reforms to ensure the integrity of meat products consumed within the United States. The legislation has evolved since the early 20th century, following Upton Sinclair's revelations about unsanitary conditions in the meatpacking industry, which led to the Meat Inspection Act of 1906 and the creation of the Food and Drug Administration (FDA) under the Pure Food and Drug Act.