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
According to the 1930 census report which contains the most recent figures available, there were nearly 12,000 graduate veterinarians in the United States, 75 per cent of whom were engaged in private practice. In the same year a study in six representative states showed that 39 per cent of the time of the practitioner was taken up with cattle, 20 per cent with horses, 20 per cent with small animals, 16 per cent with swine, 3 per cent with poultry and 2 per cent with sheep. In the ten years that have elapsed it seems reasonable to believe that these statistics would have to be modified to some extent.
Newsom, I. E.
Iowa State University Veterinarian: Vol. 4
, Article 1.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol4/iss1/1