Phenotypic and genomic analyses of agonistic interactions in laying hen lines divergently selected for feather pecking

Abstract

In poultry, aggressive pecking and threatening are normal agonistic behavior patterns which serve to establish a social hierarchy. As agonistic behavior is a stressor for animals, its excessive occurrence is undesired in layer flocks. Feather pecking is a longstanding serious problem in layer flocks and its relationship to agonistic behavior is still not clear. Therefore, phenotypic and genomic analyses of the agonistic and feather pecking behavior of two laying hen lines divergently selected for high and low feather pecking were conducted. The hens were phenotyped for the active traits aggressive pecks delivered (APD)11Aggressive pecks delivered (APD), threats delivered (TD)22Threats delivered (TD), feather pecks delivered (FPD)33Feather pecks delivered (FPD) and the passive traits aggressive pecks received (APR)44Aggressive pecks received (APR), threats received (TR)55Threats received (TR) and feather pecks received (FPR)66Feather pecks received (FPR). Indices were built by subtracting the passive traits from the respective active traits to obtain the aggression index, the threat index, and the feather pecking index. As all three behavior patterns in their excessive manifestations are undesired, the index-traits Activity and Passivity were also defined by combining each the active and passive traits. The results showed that FPD is significantly positive correlated with APD and TD in both lines, but with higher coefficients in the high feather pecking line. The average amount of FPR in both lines is nearly the same and no correlation was found between FPR and FPD, APD or TD in any of the lines. The active traits and the feather pecking index showed medium heritabilities, whereas the heritability was negligibly small for the other traits. GWAS revealed four nominal significant (p ≤ 5*10−5) SNPs for APD on chromosome 6, the same four and three additional SNPs on chromosome 8 for Activity and three SNPs on chromosome 1 for the feather pecking index. It is concluded, that selection on high feather pecking leads to an increase of agonistic behavior. The correlation probably depends on the phase of establishing the social hierarchy in which the hens in a newly formed group are at the time of observation, and might disappear, after a stable ranking is established. The reception of feather pecking is similar in both lines. GWAS revealed that TD, APD, Activity and the feather pecking index seem to be typical quantitative traits with associated regions for the latter three which have slightly greater effects on these traits than other regions in the genome.