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
Survey studies made by the United States Department of Agriculture in cooperation with the Experiment Stations of Iowa, Illinois and Indiana indicate that an average of 1.1 percent of the pigs farrowed are eaten by the sow. It is true that this is but a small percentage of the pigs lost before weaning age. However, these losses are often due to the destruction of an entire litter and by the time a sow has reached farrowing time she represents a considerable investment by the owner. The newborn killed by the vicious sow represent only a part of the loss. Pigs refused by the mother may be transferred to other litters or fed by hand which is often not as satisfactory as being mother fed. In spite of its commonplace occurrence, veterinary literature makes scant mention of this condition.
Kingrey, B. W.
"Hysteria of the Parturient Sow,"
Iowa State University Veterinarian: Vol. 17
, Article 4.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol17/iss2/4