Meat and Poultry Special Investigator ActThis bill establishes the Office of the Special Investigator for Competition Matters within the Agricultural Marketing Service's Packers and Stockyards Division. Specifically, the office must use all available tools (e.g., subpoenas) to investigate and prosecute violations of the Packers and Stockyards Act of 1921 (P&S Act). Further, the bill grants the office the authority to bring any civil or administrative action authorized by that act.Additionally, the office mustserve as a liaison to the Department of Justice and the Federal Trade Commission with respect to competition and trade practices in the food and agricultural sector,consult with the Department of Homeland Security on national security and critical infrastructure security in the food and agricultural sector, andmaintain a staff of attorneys and other professionals with appropriate expertise.As background, the purposes of the P&S Act are to assure fair competition and trade practices, safeguard farmers and ranchers, protect consumers, and protect livestock, meat, and poultry industry members from unfair, deceptive, unjustly discriminatory, and monopolistic practices. Those engaged in the business of marketing livestock, meat, and poultry in commerce are subject to the P&S Act.