Wow never heard the saliva thing before. Can’t say I believe that one. I’ve owned a horse that always had a wet bit. Ones that get a milk mustache when ridden. And another that will fling spitballs rather gross like while bing ridden. Not too sure how factual your believes are.
It absolutely is true.
“Bicarbonates in saliva buffer the gastric acid and pepsin produced by the pyloric
portion of the stomach and coat and protect the squamous epithelium in the cardiac
region. If inadequate saliva is produced by the horse, the pyloric region becomes
more acidic and the cardiac region is left unprotected from any contact with gastric acid. While gastric acid in the horse is secreted continuously with or without the presence of food (Murray, 1998), horses salivate only when chewing (Alexander and Hickson, 1970). Feeding forages to horses increases the amount of chewing time and consequently the amount of saliva produced (Murray and Schusser, 1989), and forage meals do not stimulate as much gastric acid production as grain meals (Smyth et al., 1988).”