Quantitative assessment and comparison of genetic susceptibility to colibacillosis in meat-type chickens after intratracheal inoculation of three different doses of E. coli506.

Abstract

Colibacillosis is a bacterial disease which causes substantial animal and economic losses in the broiler industry worldwide. Breeding for resistance to colibacillosis can be an important tool in reducing these losses and in complementing management strategies such as therapeutic treatment and vaccination. The aim of this study was to examine the difference in susceptibility between two pure and one commercial line of meat-type broilers after exposure to different doses of E. coli506. Intratracheal inoculation took place at 8 days of age. When the chicks were 17 days of age, the experiment was ended. Chicks of each line were divided into four equal groups that received either a low, middle or high dose of E. coli or were PBS inoculated. Susceptibility within each line was evaluated by comparing the E. coli inoculated groups to their PBS inoculated counterparts. Susceptibility to E. coli was measured in terms of mortality, growth and postmortem lesion score. Results of this experiment show a distinct dose-effect of E. coli on all those parameters. Mortality, reduction of mean weight gain and the mean lesion scores were highest in the groups that received the high concentration E. coli inoculum and lowest in the groups that received a placebo. In terms of mortality, the red chicken line was most susceptible to colibacillosis. However, the blue chicken line had comparable or higher lesion scores at post-mortem examination. Overall, the commercial chicken line showed the lowest susceptibility to colibacillosis.