C. Heak, P. Sukon, S. Kongpechr, B. Tengjaroenkul, and K. Chuachan, “Effect of Direct-fed Microbials on Intestinal Villus Height in Broiler Chickens: A Systematic Review and Meta-Analysis of Controlled Trials”, Int. J. Poult. Sci., vol. 16, no. 10, pp. 403–414, Sep. 2017, doi: 10.3923/ijps.2017.403.414.