The commission may provide the service of competent veterinarians to attend auction sales at the various public livestock markets on the day of the sale. The costs, exclusive of the pay of a veterinarian provided by the commission, of all tests, serums, vaccine, treatments, and labor furnished by the livestock auction market necessary for the enforcement of this chapter and the protection of livestock against contagious and infectious diseases must be paid for by the buyer of the livestock, and the costs constitute a lien against the animals.