Direct and correlated responses to multitrait, divergent selection for immunocompetence

Area of Science:

• Animal Science
• Immunology
• Genetics

Background:

• Leghorn chickens were previously selected for an immunocompetence index.
• This index incorporated antibody production to Mycoplasma gallisepticum (MG) and Pasteurella multocida (PM) vaccines, reticuloendothelial clearance of colloidal carbon (CCA), and phytohemagglutinin (PHA) response.

Purpose of the Study:

• To produce replicated Leghorn chicken lines with divergent multitrait immunocompetence levels via index selection.
• To characterize these lines regarding immune-response traits, trait correlations, and correlated responses in production traits.

Main Methods:

• Index selection was applied to create divergent lines for immunocompetence.
• Immune-response traits, heritability, genetic correlations, and production traits were analyzed across generations 5-7.

Main Results:

• Significant differences (P < .05) were observed between high and low immune response lines and between replicates for immune traits.
• Heritability estimates for the index and individual traits varied, with realized heritabilities showing substantial differences between replicates for some traits (e.g., CCA).
• Phenotypic correlations among immune traits were generally small, while genetic correlations varied widely. Few significant differences were noted in production traits.

Conclusions:

• Multitrait index selection effectively produced divergent immunocompetence lines in Leghorns.
• Selection for immunocompetence had minimal correlated effects on key production traits like body weight and egg production.