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 Feb. 20, 1940, a nine year old Percheron mare was admitted to the Iowa State College Veterinary Clinic. The mare had aborted nine hours previous to her admission to the clinic and was suffering from retention of fetal membranes.
Simonsen, D. W.
"A Retained Placenta in a Mare,"
Iowa State University Veterinarian: Vol. 2
, Article 13.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol2/iss3/13