Immunological parameters in meat-type chicken lines divergently selected by antibody response to Escherichia coli vaccination.

Our group has established two lines of meat-type chickens divergently selected for early (HC line) and late (LC line) antibody responsiveness at 10 days of age to immunization with inactivated pathogenic Escherichia coli bacteria. The question addressed in the study presented here is whether this selection has changed other immunological responses, increasing the overall 'early' immunocompetence. Broilers of the third and fourth generations (S3 and S4) of the selected lines (HC and LC) and a control, unselected line (CT) were vaccinated at 10 days of age with E. coli vaccine, Newcastle virus vaccine (NDV), sheep erythrocytes (SRBC) or bovine serum albumin (BSA). Line-HC chicks exhibited higher antibody titers to E. coli, NDV and SRBC than CT or LC chicks. At 20 days of age HC chicks demonstrated a higher total protein and a higher beta- and gamma-globulin levels in their serum. At 21 days of age, HC chicks cleared carbon particles faster than LC chicks. Peripheral blood lymphocytes (PBL) from HC chicks vaccinated with E. coli vaccine, proliferated in vitro more actively in the presence of the stimulating antigen than the PBL of LC chicks. Peripheral blood lymphocytes (PBL) obtained from HC-line chicks exhibited a higher proliferative response to concanavalin A (Con A)-, phytohemagglutinin (PHA)- or pokeweed mitogen (PWM)-stimulation than LC PBL. These results demonstrate that the selection for high or low antibody response to E. coli at a young age resulted also in a significant change in the response of other parameters of the immune system. The high response to E. coli was found to be associated with a high antibody response to other antigens (NDV and SRBC), increased phagocytic activity and increased proliferative response to antigen or mitogens. The selection most probably affected early immunocompetence.