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.

• Immune response
• poultry
• stress response
• social challenges
• social groups
• welfare

Acknowledgements

The authors wish to thank the excellent contribution of Iurancha González, David López, the maintenance personnel at Neiker-Tecnalia and Avícola Gorrotxategui S.L. We also thank the veterinary assistance of Ignacia Beltrán de Heredia and David Lizaso, and Dario C. Arbelo for his technical advice during leukocyte determinations. We thank the editor and two anonymous reviewers for the comments received that helped improve the quality of the manuscript.

Declaration of interest

The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper. This project was funded by the Ministry of Economy and Competitiveness of Spain (Agro resources and technologies (AGL) 2010-18276, MODELAY), including the salary of G.L. This work done while R.H.M. was on a sabbatical visit to Neiker-Tecnalia, Arkaute Agrifood Campus, Department of Animal Production, P.O. Box 46, 01080 Vitoria-Gasteiz, under an IKERBASQUE (Basque Foundation for Science, Alameda Urquijo 36-5 Plaza Bizkaia, 48011 Bilbao, Spain) visiting professor support program.

R.H.M. is a career member of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Argentina. F.N.N. holds a post-graduate research fellowship from the latter institution.