Which agency regulates the entry of dogs used in livestock handling for infectious disease checks?

The correct answer highlights the role of the Department of Agriculture - Animal and Plant Health Inspection Service (APHIS) in regulating the entry of dogs used in livestock handling for infectious disease checks. APHIS is specifically tasked with safeguarding animal health and ensuring the control of animal diseases. Their responsibilities include monitoring and inspecting livestock, as well as overseeing protocols for any animals that might enter the country, particularly in relation to zoonotic diseases and ensuring biosecurity in agricultural practices.

The involvement of APHIS ensures that any potential risks posed by infectious diseases that could affect livestock are identified and managed properly. This is crucial for both animal health and the broader agricultural industry, as it helps to prevent outbreaks that could have severe economic impacts.

While other agencies might have roles related to animal health or public safety, APHIS is the primary agency with explicit authority and focus on agriculture and animal health, particularly when it comes to infectious disease checks in livestock handling scenarios.