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 occurrence of embryonic and fetal mortality in the porcine species has continued to challenge those pursuing its epidemiology. While sporadic and endemic field cases are continually studied, a pantoscopic approach to this problem is difficult to achieve. This failure is due partly to the fact that multiple etiological agents are involved as well as the fact that less than 50% of the abortions and stillbirth cases are properly identified with a recognized etiological agent.
Evans, L. E.
"Embryonic and Fetal Mortality in the Porcine Species,"
Iowa State University Veterinarian: Vol. 28
, Article 7.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol28/iss1/7