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
A local veterinarian sent in this interesting case history of a free-martin Holstein heifer. At two years of age, this heifer appeared to have a normal sexual cycle. She had been bred six or eight times and still came in heat regularly. This heifer showed no masculinity or coarseness as do many free-martins.
Lortz, H. P.
Iowa State University Veterinarian: Vol. 4
, Article 15.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol4/iss2/15