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
The most common means of spread of many of the common endemic diseases of swine is by transmission from the dam to her offspring during the first few days of life. In the great majority of cases the swine fetus is free of all organisms until it passes the cervix. Utilizing adequate technique, pigs can be delivered surgically and removed to rearing areas without exposure to swine organisms.
Switzer, W. P.; Preston, K. S.; and Morrissey, T. J.
"Substitutes Needed For Biological Protection,"
Iowa State University Veterinarian: Vol. 25
, Article 1.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol25/iss1/1