J. Hu, H. Chen, and H.-W. Cheng, “Effect of Direct-fed Microbials, Bacillus subtilis, on Production Performance, Serotonin Concentrations and Behavioral Parameters in a Selected Dominant Strain of White Leghorn Hens”, Int. J. Poult. Sci., vol. 17, no. 3, pp. 106–115, Feb. 2018, doi: 10.3923/ijps.2018.106.115.