(a) Unless some other test is authorized in writing by the commissioner, the official test shall be the intradermic by the double injection of the caudal fold and vulva.

(b) A tuberculin test shall be applied only by an accredited veterinarian registered with the Education Department of a veterinarian regularly employed by the county, State or Federal Bureau of Animal Industry.

(c) The entire herd, or any cattle in the herd, shall be tuberculin tested or retested at such times as may be deemed advisable by the State and Federal Bureaus of Animal Industry.