The impact of phenotypic appearance on stress and immune responses in laying hens: is it a group size dependent phenomenon?

MARIN R. H.; NAZAR, F. N.; LISTE M. G.; CAMPDERRICH I.; ESTEVEZ I.

Vitoria-Gasteiz

Congreso; 48th Congress of the International Society for Applied Ethology; 2014

International Society for Applied Ethology

Alteration of birds? phenotypic appearance (PA) may lead to unwanted behaviors, potentially impairing poultry welfare, health and productive performance. Likewise, group size (GS) may play an important role modulating the expression of adaptive behaviors and stress response. This study evaluated whether manipulation of the PA and GS in Hy-line Brown laying hens may affect stress response and immune function. At 1 day of age, 750 chicks were randomly assigned to 30 pens at GS either 10 or 40 (8 hens/m2). At arrival, PA of 0, 30, 50, 70 or 100% of the birds in each pen were artificially altered by black dying their heads back (Marked-M). Remaining birds remained unchanged (Unmarked-UM). At 32 weeks, basal and acute stress adrenocortical response, heterophil/lymphocyte (H/L) ratio, lymphoproliferative response to phytohemagglutinin-p and primary antibody response against sheep red blood cell were measured in 6 birds/pen (3 M and 3 UM within the PA heterogeneous pens and 6 M or 6 UM from homogeneous pens). No differences were found among the initial treatment combinations. In a second phase, birds in initially homogeneous pens (0 and 100%), were either M or UM sequentially to reach 30, 50 and 70% of the hens altered at 34, 38 and 44 weeks, respectively. Initially heterogeneous pens remained unaltered and were used as controls. Two weeks after the PA manipulations (46 weeks), mentioned variables were measured again. Both altered and non altered hens within altered pens showed increased H/L ratios compared to their unchanged control counterparts. These results suggest that the appearance of new phenotypes triggered a social chronic reaction in all pen members whether altered or unaltered. After a social isolation test, all hens showed an increased plasma corticosterone response. However, within GS 40, the hens that remained with their PA unaltered evidenced a significantly lower response than their PA altered groupmates. This result suggest that in GS 40, unaltered hens within altered pens were able to better cope when exposed to a new social stressor probably due to previous experience that may potentially enhance social plasticity favored by social interactions emerging after the PA alterations of their groupmate counterparts. Although all birds in altered pens showed modified blood cell populations, antibody and lymphoproliferative responses showed no differences between PA altered and unaltered hens suggesting that all groupmates were able to immunologically cope with the chronic social stress induced at least within the time frame evaluated.