The Effect of the Sex-Linked Dwarfing Gene, dw, on the Immune Responses of Broiler Breeder Chickens

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Two generations of a normal (AG) strain and a dwarf (D2) strain and one generation of an F1 (AG × D2) cross-strain of broiler breeder chickens were evaluated to determine if the sex-linked dwarfing gene, dw, affects specific immune competence parameters. The lymphocyte blast transformation response using the mitogen phytohemagglutinin-M was significantly stronger among second generation dwarfs compared to either normal or cross-strain birds.A delayed-type hypersensitivity response was induced by intradermal injection of tuberculin into the wattles of sensitized birds. Dwarf and cross-strain birds had significantly larger wattle swelling indices than normal strain birds. Dwarf males and cross-strain females had significantly stronger tuberculin responses than normal strain birds of either sex at 24 and 48 hr postchallenge. In addition, the tuberculin response of normal strain birds decreased significantly between 24 and 48 hr following antigenic challenge, whereas the tuberculin responses of cross-strain birds increased and dwarf birds remained the same.The dwarfing gene had no significant effect on natural agglutinin titers to 1% rabbit red blood cell (RRBC) in either the parent or second generation. There was also no significant difference in the response of parent generation birds to sheep red blood cells (SRBC) following intravenous sensitization with 1 ml of a 1% SRBC suspension. However, second generation dwarfs had significantly lower SRBC titers than normal or cross-strain birds.Assays of cellular and humoral immunity indicated that sex-linked dwarfs may have more competent T-cell subpopulations and weaker B-cell reactivity compared to normal strain birds.