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 method is proposed in which the bull is sterilized by caudal epididymectomy and rendered unable to copulate by closing the preputial orifice and establishing a small fistula between the preputial cavity and the ventral surface of the sheath for urine egress.
Shires, G. M. H.
"Another Surgical Method of Preparing Heat-Detector Bulls,"
Iowa State University Veterinarian: Vol. 39
, Article 4.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol39/iss2/4