On and after July 1, 1976, the age for official vaccination of calves with Strain 19 Brucella Vaccine shall be as follows: All heifers, regardless of breed--2 to 6 months (60 through 179 days) old; Heifers vaccinated after July 1, 1976, older than 179 days will not be eligible for indemnity if found to be reactors on a blood test after the animal is 24 months old.