By Steve Boyles
Ruminants secret enormous quantities of saliva from eight types of glands. The secretions are serous (watery), mucus or mixed. The mixed secretions are weakly buffered while the others are strongly buffered with bicarbonate and phosphate. Saliva moistens and lubricates food and assists in masticating (chewing) and swallowing. Saliva contributes more than 70% of the water and most of the salts to the rumen. It assists in stabilizing rumen pH and provides sources of nitrogenous and mineral nutrients for the microorganisms.
Saliva is secreted as different rates during resting, eating or rumination. As the water content of the feed increases, the amount of saliva decreases. Generally feeds that increase salivation during eating increase salivation during resting and rumination. Feeds that do not induce large quantities of saliva to be secreted are those with either low dry matter content (lush pasture) or those eaten rapidly such as ground or pelleted hay or grain concentrate. The slowest rates of secretion occur after feeding ceases and then gradually increases reaching its highest rate before the next feeding.
The principal organic constituents of saliva are mucus and urea. Urea nitrogen comprises about 77% of total nitrogen in saliva. The organic constituents of saliva, principally mucous and urea are an important source of nitrogen for the rumen microorganism and help promote an active microbial population in the rumen. The recycling of urea through saliva is an important mechanism for conserving nitrogen and recycled urea may amount to 10% of the nitrogen in the diet. Undoubtedly several of the mineral needs of rumen microorganisms are supplied by saliva.
Saliva facilitates mastication of food by softening it and aids in swallowing food by making it slippery. Though not major, saliva also offers some buffering capacity to maintain pH levels for rumen microorganisms. Saliva can work as an antifoaming agent to reduce the incidence of bloat. Chronic bloating cattle maybe what we call “Dry Rumens”. These are cattle that produce relatively low levels of saliva.
Source : osu.edu