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
On October 10, 1957, twin Holstein heifer calves were admitted to Stange Memorial Clinic. Both calves had umbilical hernias of almost identical size, and from involvement and connective tissue deposition appeared to have been present about the same length of time. In fact, the hernias were probably present at birth and of hereditary origin.
"Umbilical Hernias in Twin Calves,"
Iowa State University Veterinarian: Vol. 20
, Article 11.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol20/iss1/11