Causal effects between fructooligosaccharides (FOS) addition in diets, IgA flow rate of saliva per rat submandibular gland tissue weight, weight of cecal tissue, weight of cecal digesta, pH in cecal digesta, and IgA concentration of cecal digesta using Bayesian network analysis. Causes and effects are indicated by arrowheads and lines, respectively. The Bayesian network showed that the IgA flow rate of saliva per weight of submandibular gland tissue was affected by SCFA concentration in cecal digesta, weight of cecal digesta and addition of dietary FOS. On the other hand, the IgA concentration in cecal digesta and the IgA flow rate of saliva per weight of submandibular gland tissue were not causally related.