The National Poultry Improvement Plan (NPIP) was established in response to a need to control diseases whose existence was incompatible with the development of a modern poultry industry. Several important disease organisms are transmitted vertically from hens to chicks through the eggs. This makes the spread of the diseases almost impossible to control.
In the early 1900s, two of the important disease organisms with which most breeding flocks were infected were Salmonella pullorum, which causes Pullorum disease, and Salmonella gallinarum, which causes Fowl Typhoid.