Interference betweengenotypes from theperitonitis syndrome given simultaneously to productive SPF White Leghorn hens by intratracheal inoculation.

Abstract

The purpose of the present study was to examine if potentiation of mortality occurred after simultaneous administration of severalgenotypes, each capable of inducing theperitonitis syndrome, in comparison with single genotype application. Five groups of productive specified pathogen free White Leghorn hens were housed in isolators. Groups 1-4 consisted of 32 hens each, group 5 of 10 hens. At 32 weeks of age all groups were inoculated intratracheally. Groups 1 and 2 were inoculated with a mix of fourgenotypes and groups 3 and 4 with a mix of four other genotypes. Groups 1 and 3 were given 1 median lethal dose (LD) of each genotype per hen and groups 2 and 4 had a dose of 0.1 LDper genotype per hen; group 5 was mock inoculated. The experiment ended one week after inoculations. In Group 5, no mortality occurred and gross lesions were absent atexamination. Mortality in groups 1 and 3 was 84% and 81%, respectively; in groups 2 and 4 59% and 66%, respectively. Although mortality in groups 1 and 3 exceeded the expected 50%, this could not be due to potentiation as cluster analysis of reisolates showed that in individual hens only one genotype was found, indicating interference betweengenotypes. In groups all four or only two genotypes were recovered, showing that not all genotypes will induce colibacillosis in all experimental groups. Therefore, broad protection can be best assessed by challenging with various single genotypes.All four or only twogenotypes were found in groups of hens given mixes of four genotypes.In contrast, only one genotype was found in individual hens.genotypes interfere with each other in hens after given as a mix.Interference is likely based on a random process.Broad protection can best be assessed by challenging with single genotypes.