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
This group of disorders comprises disease conditions in which infections or transmissible agents cannot be demonstrated and which are often benefited by minor changes in the ration. According to statistical data the percentage of cases falling under this heading is comparatively high, a fact which is surprising as feeding of poultry is fairly well standardized. It is not definitely known to what extent factors of management, such as brooder temperature, space, and ventilation influence the appearance of nutritional diseases. Our ignorance of the importance of congenital factors in the development of nutritional maladies is often cloaked under such expressions as "weak stock" and "lack of vitality" which cannot be determined by field or laboratory diagnosis.
Lee, C. D.
Iowa State University Veterinarian: Vol. 4
, Article 5.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol4/iss2/5