Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
There are many diseases including those affecting only reproduction that can be spread by the bull when used for artificial insemination or for natural service. The bull is one half of the herd, therefore great precautions should be exercised in assuring the owner that the bull he adds to his herd is disease free. When artificial insemination is used, equal precautions must be followed to provide disease free semen.
"Health Examination of a Bull,"
Iowa State University Veterinarian: Vol. 18
, Article 5.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol18/iss1/5