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 seems to be either an acute, sudden-death syndrome or the subclinical, asymptomatic condition seen only at the time of slaughter. Generally only one pig in a herd dies, but losses do vary from a single pig to approximately 50% death loss do occur with stress from management or environmental changes, other changes, other disease, or immunization. One slaughter house observation (representing the subclinical syndrome) reported a 53% incidence. Another similar study of 443 slaughtered hogs showed 86% abnormal cornification of stomach linings, which is an early stage of any beginning ulcer.
"Incidence and Etiology of Gastric Ulcers in Swine,"
Iowa State University Veterinarian: Vol. 26
, Article 5.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol26/iss3/5