If the veterinarian authorized by the commissioner to examine or test an animal for the presence of an infectious or contagious disease certifies to the commissioner in writing that he has made an examination or test in accordance with the rules adopted by the commissioner, that in his judgment such animal is infected with a specific infectious or contagious disease, or that its destruction is necessary in order to prevent or suppress, or to aid in preventing or suppressing such disease such animal shall, except in cases herein otherwise provided, forthwith be slaughtered by and at the expense of the owner or the person in possession thereof, and the carcass shall be dealt with as provided for the disposal of carcasses of imported animals after slaughter.