Genetics of immunocompetent traits in a synthetic broiler dam line.

Three hundred and three chicks of both sexes, from a synthetic dam line (SDL) of broiler chickens, were studied for economic traits (body weights at 4, 5 and 6 weeks of age) and immunological traits (humoral and cell mediated immune responses, and serum lysozyme concentration). The objective was to evaluate these traits and to estimate their genetic and non-genetic parameters. The humoral immune response was assessed by estimating the antibody response to sheep red blood cells using the haemagglutination (HA) test and serum IgG concentration using single radial immunodiffusion (SRID). The cell mediated immune (CMI) response was estimated as in vivo response to a mitogen (PHA-P). Serum lysozyme was measured by lysoplate assay. Least squares means for body weight at 4, 5 and 6 weeks were 684 +/- 20, 920 +/- 19 and 1205 +/- 28 g, HA titre was 6.289 +/- 0.246, CMI was 0.438 +/- 0.015 mm, lysozyme was 1.860 +/- 0.047 microg/ml and IgG was 6.287 +/- 0.194 mg/ml. There was an effect of sire on HA titre and on body weight at 4, 5 and 6 weeks of age; males were heavier than females. Heritability estimates were high for body weights but low for immunological traits. Phenotypic correlations (rp) among body weights were high and positive but were very low between body weights and most immunological traits. Among the immunological traits all rp were very low. Genetic correlations (rg) of body weights were positive and medium to high with CMI and HA and negative with serum IgG.