Immune competence, resistance to Escherichia coli and growth in layer parent chicks as influenced by dietary protein levels

The immunocompetence, resistance to Escherichia coli and growth in layer parent chicks were evaluated in the diet having three levels of dietary crude protein (CP) viz. 16%, 18% and 20% and these diets were referred as low-, medium- and high-protein diet respectively. Body weight gain and feed conversion ratio did not differ significantly among the dietary groups. At 5 days post inoculation (PI), the antibody titre was significantly higher in low protein dietary group compared to medium and high protein dietary groups. When SRBC was injected at 14 days of age, at 10 days PI no significant differences were observed among the dietary groups. At 15 days PI, the antibody titre was significantly higher in low and high protein dietary groups than those of medium protein dietary group. When SRBC was injectedat 28 days of age, the antibody titre was significantly higher in the chicks fed diet with low protein compared to those fed with medium and high protein diet at 5 days PI, but no differences were observed at 10 and 15 days of PI. There was no significant difference in antibody production at 5, 10 and 15 days of PI among the dietary groups when SRBC was injected at 42 days of age. Highest antibody titre was found at 10 days post inoculation, when SRBC was injected at 42 days of age in all dietary groups.The CBH response measured as thickness of wattle in response to PHA inoculation of chicks was similar in all the groups irrespective of the levels of dietary protein at 56 days of age. When E. coli was injected at 28 days, no significant differences were found in the lesion score of the chicks fed different diets. Significant difference for percent relative spleen weight was not observed among the dietary groups, however the relative weight of bursa was significantly higher in the chicks fed low and high protein diet than those fed medium protein diet. The lesion score, percent relative weight of spleen and bursa did not differ significantly, when E. coli was injected at 42 days of age.