The influence of genotypes and social ranks in the clinical course of an experimental infection with Mycoplasma pulmonis (MRM) in inbred rats.

Social ranks of healthy, adult male inbred rats housed in groups of four per cage were determined by their relative differences in intromission and ejaculatory patterns observed repeatedly under competitive copulatory conditions. Once ranked they were inoculated with M. pulmonis by contact with castrated females suffering clinically from M.pulmonis.--Body weight reduction and scores for laryngo-bronchotracheal breathing sounds and dispnoea or sneeze or wipe and the titers of specific antibodies were continuously observed during 123 days of illness. Studies were done in five series concerning the inbred strains AS/Ztm, LEW/Ztm, BH/Ztm. Genotypic differences accounts for 60-80% of the variability of the illness. LEW/Ztm was the most affected strain. Only in strain LEW/Ztm week correlations were shown between social rank before the infection (characterized by sexual activity under competitive conditions) and the scores for breathing sounds, dyspnoea and sneeze and wipe. Animals high in social rank showed a milder clinical course of the infection.