The current study finds no signs of distinct coping styles being consistent to large or to small individuals at any age or under any feeding regimen. It shows, however, that small broiler breeder females display a more active stress response with lower levels of fearfulness and a heightened social motivation compared to large broiler breeder females at 4 weeks of age and further indicates that lower levels of fearfulness is also present in small every day fed 18 week broiler breeder females. Hence there is no indications that small broiler breeders would experience lower levels of welfare under the current management practice, rather it indicates that small individuals may be better able to cope with the challenging, multi-bird environment in which they are reared.  

Future studies should focus on behavioural and physiological differences at a very early age in order to further investigate what traits are involved in the development of growth heterogeneity. It would also be further interesting to investigate whether the increased level of social motivation found in small individuals in this study may have a clear positive influence on the welfare of these individuals. Do a small body size and increased social tolerance benefit these individuals when coping with the potential stressors of feed restriction and excessive social stimuli?