title: Manipulation of the phenotypic appearance of individuals in groups of laying hens: effects on stress and immune-related variables.
abstract: This study evaluated whether phenotypic appearance (PA) alteration during two developmental phases in laying hens, reared in two different group sizes, affects stress and immune responses. After hatching, 750 chicks were randomly assigned to 30 pens at a group size of either 10 or 40 birds. Then, the appearance of 0, 30, 50, 70 or 100% of the chicks in each pen was altered by blackdyeing their head feathers (marked); remaining chicks were unmarked. At 32 weeks, basal and postacute stress plasma corticosterone concentration, leukocyte counts, phytohemagglutinin-p lymphoproliferative and primary antibody responses were measured in six birds/pen. Analysis of variances (ANOVAs) showed no differences among treatment combinations. In a second phase, birds within initially homogeneous pens were sequentially either marked or had dye bleached to alter PA of 70% of hens in each flock (= group in a pen). Hens within initially heterogeneous pens remained unaltered as controls. The above variables were remeasured. Hens in phenotypically manipulated pens showed modified leukocyte counts compared to hens in control pens, indicating a chronic stress reaction in all penmates (whether individual PA was altered or not). Social isolation increased plasma corticosterone concentration. However, within groups of n = 40, phenotypically unaltered hens had lower responses than their altered penmate counterparts, suggesting that remaining in a stable PA group aids better coping with challenges. Although all hens in manipulated pens showed modified leukocyte counts, their antibody and lymphoproliferative responses did not differ from controls suggesting that all groupmates were able to immunologically cope with the challenges presented, within the timeframe evaluated.
authors.affiliation: a Instituto de Investigaciones Biológicas y Tecnológicas (IIByT; CONICET-UNC) and Instituto de Ciencia y Tecnología de los Alimentos (ICTA), Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba , Córdoba , Argentina .
authors.forename: F N
authors.initials: FN
authors.lastname: Nazar
authors.affiliation: a Instituto de Investigaciones Biológicas y Tecnológicas (IIByT; CONICET-UNC) and Instituto de Ciencia y Tecnología de los Alimentos (ICTA), Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba , Córdoba , Argentina .
authors.forename: R H
authors.initials: RH
authors.lastname: Marin
authors.affiliation: b Department of Animal Production , Neiker-Tecnalia, Arkaute Agrifood Campus , Vitoria-Gasteiz , Spain, and.
authors.forename: G
authors.initials: G
authors.lastname: Liste
authors.affiliation: b Department of Animal Production , Neiker-Tecnalia, Arkaute Agrifood Campus , Vitoria-Gasteiz , Spain, and.
authors.forename: I
authors.initials: I
authors.lastname: Campderrich
authors.affiliation: b Department of Animal Production , Neiker-Tecnalia, Arkaute Agrifood Campus , Vitoria-Gasteiz , Spain, and.|c IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3 , Bilbao , Spain.
authors.forename: I
authors.initials: I
authors.lastname: Estevez
mesh_terms: D000818:Animals; D002645:Chickens / Q000502:physiology*; D003116:Color; D003345:Corticosterone / Q000097:blood*; D005260:Female; D006799:Housing, Animal; D010641:Phenotype; D010835:Phytohemagglutinins / Q000276:immunology*
chemical_list: D010835:Phytohemagglutinins; C028784:phytohemagglutinin-P; D003345:Corticosterone
keywords: Immune response; poultry; social challenges; social groups; stress response; welfare