Complete mastication occurs via regurgitation while the cow is resting or after eating.
Mastication rate varies with the level of hunger and the nature of the feed, but averages at 40,000 to 45,000 chews per day. Rumination involves regurgitation of ingesta from the reticulo-rumen, swallowing of the regurgitated liquids, remastication of the solids accompanied by salivation and swallowing of the newly formed bolus. These populations are mixed species of bacteria which respond to the changing diets offered to the animal. The microorganisms multiply and grow, and as they do they produce protein and by-products such as volatile fatty acids and vitamins which can be used by the host animal. The number of microorganisms is dependent on the amount and nature of the diet, the frequency of feeding, rumination, physical distribution and quantity of protozoa and bacteria, and the species of the host animal.