Rumen volume, saliva flow rate, and systemic fluid homeostasis in dehydrated cattle

This work was carried out to test the hypothesis that the high level of salivary secretion containing much Na+ and the volume of fluid sequestered in the foregut of ruminants play an important part in water and Na+ homeostasis. Saliva flow and composition and water and Na+ balance in the rumen have been measured in hydrated and dehydrated cows with esophageal fistulas. Reduction of voluntary feed intake in beef cattle during water deprivation was related to the stage of dehydration. Salivary secretion rate was linearly related to voluntary feed intake (r = 0.96) and inversely and linearly related to plasma osmolality (r = 0.88). The reduction in the volume of water stored in the rumen contributed to the major portion (55%) of the total water loss. Utilization of gut water attenuated the rise in blood plasma osmolality, and this may be connected with an animal's ability to continue eating despite dehydration.