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In large-scale poultry farming injurious pecking causes significant economic damage worldwide. In commercial turkey flocks, especially in the case of male turkeys, this behaviour raises serious welfare issues in addition to economic losses. The present study aimed to better understand the environmental factors involved in the development of this condition. Therefore, the stress condition resulting from pecking behaviour was investigated by using feather and blood plasma samples and animal welfare indicators.

Four experimental groups were established, of which the fourth group was the control. In the first room, the light intensity was 100 lux instead of the standard technologically recommended 40 lux, and in the second room, the room temperature was 10% higher than the standard for the entire duration of the experiment. In the third room, the stocking density was 3.5 birds/m2 compared to 2.5 birds/m2 in the other groups. Apart from the single modifications mentioned above, the rooms did not differ. Feathers and blood were sampled from trial birds on four occasions. From these samples, cortisol was quantified by a competitive ELISA test. During the experiment, data were recorded in the groups according to the AWIN Welfare assessment protocol for Turkeys, 'Appendix A and B', 2015.

Based on results from feather samples, the mean cortisol concentrations in Group 2 were significantly higher than in the other three groups at the first and second sampling times. For cortisol concentrations from blood plasma samples, at the second sampling time, we found a significant increase in Group 2 and Group 3 compared to the control. In addition, at the third sampling time, significantly higher values were found in Group 1 compared to the means of the other three groups. When evaluating the scores from the AWIN protocol, Group 3 showed significantly higher scores (lower welfare status) for the factor related to social behaviour and aggression-related injuries compared to the other two groups. The factor related to illness and mortality was also significantly higher in group 3 compared to the control and Group 1.

In summary, there were significant differences at different time points in all three experimental groups. While the results of feather and blood plasma samples were significant in Group 2, the results of blood plasma samples and the AWIN protocol were significant in Group 3. Thus, it can be assumed that the presence of aggressive behaviours, at the time of some measurements, was substantial in these groups. However, it should be noted that birds in Group 1 also have shown increased aggressive behaviours temporarily.