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 coccygeal vein in the tail can be a convenient place from which to obtain a blood sample. This method is used mostly in dairy cows. Stock cows usually are not as well adapted for the use of this technique unless they are accustomed to being handled and are fairly docile; however, this technique can be used if there are only a few cows and if no chute is available. It is gratifying to hear farmers comment that the cows don't seem to mind at all. Many dairy farmers do not like the use of the nose lead and certainly most cows will resist vigorously.
"Tail Bleeding in the Bovine,"
Iowa State University Veterinarian: Vol. 23
, Article 5.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol23/iss1/5