There are many agencies within the United States Department of Agriculture (USDA), but two that are of particular interest to those in the food industry are the United States Department of Agriculture Food Safety and Inspection Service (FSIS) and the Agricultural Marketing Service (AMS). While both agencies fall under the USDA umbrella, they each have different areas of focus.
The FSIS is responsible for ensuring that the nation's commercial supply of meat, poultry, and egg products is safe, wholesome, and correctly labeled. The agency inspects all animals slaughtered for human consumption and all meat, poultry, and egg products before they enter interstate commerce. In addition to inspections, FSIS also regulates slaughterhouses and processors through performance-based regulation. This means that rather than dictating specific processes or procedures that businesses must follow, FSIS establishes food safety standards and then monitors businesses to ensure they are meeting these standards.
AMS on the other hand focuses on promoting fair marketing practices for agricultural commodities and ensuring an adequate supply of high quality foods for consumers. AMS also develops voluntary quality grading standards for certain commodities as well as administers programs like the Federal Meat Inspection Program which provides inspection services to producers who sell their products interstate. Other programs administered by AMS include the National Organic Program which sets standards for organic labeling of agricultural products, as well as the Egg Products Quality Control Program which ensures eggs sold in interstate commerce meet minimum quality requirements.
So while both USDA agencies work to protect public health by regulating different aspects of our food supply chain, it's clear that their focus is quite different. The FSIS is focused on inspecting food products to ensure they meet food safety standards while AMS works to develop quality standards and oversee programs related to marketing practices and commodity supplies.