Experimental infections were set up in commercial laying birds, comprising a white relatively resistant line and a red susceptible line infecting with Salmonella enterica serovar Gallinarum. The major findings were that in susceptible birds clinical disease occurred in a dose-dependent manner. Faecal excretion occurred in susceptible birds almost up to death but also occurred in the more resistant line and in birds, which were convalescing. Removal of birds, which had died from the disease, from the environment, reduced the resultant mortality/ morbidity and may be regarded as a useful measure for control.

Although the epidemiology of fowl typhoid in chickens supposedly involves a vertical transmission stage, a previous work run by the authors has suggested that this did not happen in a commercial line of laying hens highly susceptible to systemic disease with Salmonella Gallinarum. A new experiment was carried out in two other lines of commercial layers, considerably more resistant than those used in the previous study. Clinical fowl typhoid was not observed, but Salmonella Gallinarum was isolated from the spleen and liver four weeks after infection and, sporadically, from the ovary.

Isopathy is low cost and non-toxic. It may have a role to play in the widespread problem of Salmonella in poultry. Further research should be conducted.

This study was carried out to assess the ability of competitive exclusion and a mixture of organic acids to prevent Salmonella infection by contact between newly hatched chicks. A bird infected with Salmonella was placed in a box containing non-infected birds, previously treated with a broth culture of faeces of adult birds (CE) and/or a mixture of organic acids. The number of Salmonella organisms in the caeca of the contact birds was estimated at 4 and 8 days post-challenge. The birds were infected with Salmonella Typhimurium, Salmonella Enteritidis (both repeated 5 times), Salmonella Agona and Salmonella Infantis (3 repetitions). The same approach was used to test the mixture of organic acids alone. In this case the birds received feed containing 0.8% of a mixture of formic acid (70%) and propionic acid (30%). Also, a third trial was carried out with birds inoculated with the broth culture of faeces and fed with feed containing the mixture of organic acids. Appropriate controls were included. Whereas the birds from the control groups and the groups treated with the mixture of organic acids were heavily infected with Salmonella, those pre-treated with CE or CE plus the mixture of organic acids had no viable cells per gram of caecal contents.

An experiment was carried out to investigate the biology of Salmonella Pullorum in two varieties of laying hens, from 5 days of age up to 9 months. One variety was resistant to systemic salmonellosis (light layers producing white 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 disappeared, but postmortem examination revealed persistent gross pathological changes in the liver, spleen, heart and ovary. The rapid agglutination test detected reactors throughout the experiment, with the strongest agglutination from 1 to 7 months post-infection. S. Pullorum was isolated from some of the organs and the eggs laid throughout the experiment. The relationship between white birds and S. Pullorum was less intense, and there were no noticeable signs of disease. There were few gross pathological changes, and the bacteria were isolated infrequently and only for a brief period after infection, although contaminated eggs were laid by these birds. The strongest serological response in the white chickens occurred between the second and the fifth month post-infection.