Immunocompetence and resistance to marble spleen disease of broiler- and layer-type pure lines of chickens.

The intent of this study was to evaluate, under concurrent conditions, cert ain responses that may be important in chicken breeding and growing. Three commercial broiler pure lines (A, B, and C) and two experimental White Legh orn lines selected for high (HAS) and low (LAS) antibody response to sheep red blood cells were evaluated concurrently for humoral and cell-mediated i mmunocompetence, resistance to marble spleen disease virus (MSDV), relative asymmetry (RA), and comb weight. Chicks were injected with 0.1 ml of 0.25% SRBC at 21 days of age. Antibody response 6 days after injection was highe st in line HAS. Titres for the commercial lines were similar to those in li ne LAS. The cutaneous basophil hypersensitivity test, an in vivo cell-media ted immune response, was measured as the increase in toe-web thickness 24 h after an injection with T-cell mitogen phytohaemagglutinin (PHA)-P or -M i nto a sample of chicks at 9 days of age and a different sample of chicks at 20 days of age. PHA-P elicited greater responses than PHA-M at both ages. The pattern among stocks, however, differed depending upon age. Responses a t 9 days were greater for the Leghorn than broiler lines, while at 20 days, responses were greater in lines A and LAS than in lines B, C, and HAS. Res istance to MSDV challenge differed among stocks, with the ranking for resis tance being C > (A = B = LAS) > HAS. Rankings of RA for normal thickness of the toe web between the third and fourth digits at 9 days of age were (HAS = LAS) > (A = B = C). There were no differences in RA among stocks at 20 d ays of age. There was a significant line by sex interaction for relative co mb weight, due to differences between lines for males but not females. Data from this study suggest that competence in one arm of the immune system is not a reliable measure of general immunocompetence, nor is it a measure of resistance in general.