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
In the past, when a swine unit wanted to eradicate a certain disease such as Pseudorabies, costly depopulation/repopulation was the only viable solution. Depopulation, facility cleanup, and repopulation is not always successful because nearby herds with a lower health status my provide a source for reinfection. In 1980, Tom Alexander of Cambridge University developed a system for producing pigs 'free of certain diseases without costly depopulation.
Swalla, Rick and Uhlenhopp, Eldon K.
"Modified Medicated Early Weaning,"
Iowa State University Veterinarian: Vol. 54
, Article 17.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol54/iss2/17