ABSTRACT
Phosphate absorption from the digestive tract increases as dietary P043-rises, and is stimulated by 1,25(OH)2D (like Ca2+ and Mg2+). Approximately 60-70% of dietary P043-is absorbed by active transport utilizing a Na+/(HP042-/H2P04-) cotransporter, and by passive diffusion. Absorption is thought to take place principally in the forestomaches of ruminants, from the large intestine of horses, and from the duodenum and jejunum of most other animal species. Parotid saliva in ruminant animals contains high levels of inorganic phosphate, which buffers protons dissociated from volatile fatty acids. High fiber diets typically increase, while concentrated rations decrease salivary phosphate secretion.
