The compatibility of economic efficiency and animal welfare is a major challenge given the increasing demand for animal-based foods. Various studies have shown that it is possible to promote the resistance and robustness of commercial poultry (primarily broilers) by modifying incubation temperatures. Focused on the histology of the Bursa fabricii , an important lymphatic organ in birds, the investigations in this paper aim to show whether short-term temperature changes during final incubation (+1 °C, 2 h/incubation day 17–20) could have an influence on the robustness of broilers compared to conventionally incubated ones. Overall, however, the temperature stimulation during final embryonic development did not result in any statistically significant morphological changes in the bursa or in the heterophil-to-lymphocyte ratio (HLR) that would clearly indicate improved immune function. However, there are obvious sex-specific differences. For instance, a sexual dimorphism could be seen in the parameters of follicle number, follicle density and in the HLR when looking at the absolute numbers. Calculation of the effect size using Cohen’s d showed that there was an effect on the relative weight of the Bursa fabricii (d = −0.28, d ♂ = −0.25, d ♀ = −0.35) cell density (d ♀ = −0.32), follicle density (d ♀ = 0.37) and the HLR (d = 0.24, d ♂ = 0.43), so that further investigations should be encouraged.
Ahlig et al. (Tue,) studied this question.