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
The emasculation of various members of the animal kingdom to suit the convenience and needs of mankind has been practiced for unknown centuries. Egyptians, Phoenicians, Greeks, Romans and the ancient Jews possessed this knowledge and Moses spoke of it in the Bible - Leviticus, Chapt. XXII, Verse 24.
Carmen, Grant M.
"Cryptorchidism in the Horse,"
Iowa State University Veterinarian: Vol. 13
, Article 3.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol13/iss1/3