Indian Journal of Poultry Science

This study was aim to assess the disease resistance status of broiler chicken lines against avian pathogenic strain of E.coli, which was selected divergently over two generations (G0, G1 and G2) of selection for immunocompetence (IC) by combining the immune response traits in to index viz., Humoral mediated immune response (HMI) to Sheep red blood cells (SRBC), cell mediated immune response (CMI) to phytohaeagglutination- P mitogen (PHA-P), levels of serum serum immunoglobin- G (IgG) and serum lysozyme level (LZM). There was significant (P<0.05) differences in all immunological traits between the generation and among the lines over two generations of bidirectional divergent selection (G₁ and G₂). A Comparatively higher value of immunological traits and IC- index values were observed in the high IC-index lines (HIL) as compared to the low IC-index lines (LIL) in the two generation of divergent selection. The challenged birds (n= 16) at 6 weeks of age showed the typical symptoms of E.coli infection viz., dullness, whitish diarrhea as compared to the control birds which remained healthy thorough out the experiment. The overall percent mortality rate in high and low index lines was 75.00 and 50.00, respectively with the pathogenic E.coli challenge. Whereas the sexual dimorphism has been observed significantly among the males and females of the both lines with 100% in all the females of high index line as compared to the low index lines (50%) and 50% mortality were observed in males of both the lines. The mean survival time (MST) was higher in low index line (7.00±1.149) as compared to the low index line (5.250±1.149). The present challenge study experiments revealed that the high index line were more susceptible to bacteria (E.coli) than the low index line over three generation of divergent selection to general immunocompetence status and further suggest that the divergent selection of low index lines would favor the higher immune response to E.coli.