Experimental Salmonella enterica serovar Pullorum infection in two commercial varieties of laying hens

An experiment was carried out to investigate the biology of Salmonella Pull orum in two varieties of laying hens, from 5 days of age up to 9 months. On e variety was resistant to systemic salmonellosis (light layers producing w hite eggs) and the other was considered susceptible (brown layers producing brown eggs). The brown birds were more affected by the infection, showing signs of clinical disease in the first month of life. Later, these signs di sappeared, but postmortem examination revealed persistent gross pathologica l changes in the liver, spleen, heart and ovary. The rapid agglutination te st detected reactors throughout the experiment, with the strongest agglutin ation from 1 to 7 months post-infection. S. Pullorum was isolated from some of the organs and the eggs laid throughout the experiment. The relationshi p between white birds and S. Pullorum was less intense, and there were no n oticeable signs of disease. There were few gross pathological changes, and the bacteria were isolated infrequently and only for a brief period after i nfection, although contaminated eggs were laid by these birds. The stronges t serological response in the white chickens occurred between the second an d the fifth month post-infection.