What is the USDA's criteria for states or zones to gain bTB Free Status?

The criterion for states or zones to gain bTB (bovine tuberculosis) Free Status under USDA regulations is based on the requirement of zero herd prevalence. This means that for a state or zone to be classified as free from bTB, there must not be any reported cases of the disease within herds. Achieving zero herd prevalence is an essential goal in controlling the spread of bTB, as it indicates that the infection is not present, allowing for safer trade and movement of cattle between regions.

The other options provided relate to prevalence levels that might indicate low bTB cases, but they do not meet the rigorous standard required for full Free Status. The focus on zero prevalence underscores the importance of completely eradicating the risk of transmission within cattle populations before a classification of freedom from the disease is granted.