This action adopts as a final rule, with changes, an interim rule that amended the brucellosis regulations to, among other things, reduce the amount of testing required to maintain Class Free status for States that have been Class Free for five or more years and have no Brucella abortus in wildlife. This document amends the interim rule to change the age at which cattle and domestic bison are included in herd blood tests from 6 months to 18 months of age for all sexually intact cattle and domestic bison, except when conducting herd blood tests as part of affected herd investigations or other epidemiological investigations. In addition, the rule allows certain States the option of either conducting brucellosis ring tests and participating in the slaughter surveillance program or developing an alternative surveillance plan that would have to meet or exceed the level of disease detection provided by combined brucellosis ring testing and slaughter surveillance testing. The rule also makes several minor changes in order to clarify the regulations. These changes are necessary to create flexibility in the brucellosis program, to refocus resources to control and prevent the spread of brucellosis, and to protect and maintain the economic viability of the domestic livestock industry.