Post-Prandial Ionic and Water Exchange in the Rumen

Abstract

SUMMARY Following the feeding of 350g. of lucerne chaff, changes in ruminal osmolality and solutes were examined. After feeding, the concentration of most ruminal ions and the osmolality rose initially. The ruminal changes were followed by a rise in serum osmolality which was maintained for 8 hr. After the initial period, the concentration of all ruminal ions fell abruptly, this fall being associated with an increase in ruminal volume, a fall in ruminal osmolality and an additional rise in serum osmolality. These changes were ascribed to an inflow of water across the ruminal wall. Ruminal infusions of NaCl and glucose appear to confirm this conclusion. Measurements of ruminal volume and omasal flow rates showed a biphasic pattern and this pattern could be related to rumination. Total daily reticulo-omasal flow (t½ = 3½ hr.) was higher than expected from pen-fed sheep, and this was assumed to be due to the pattern of feeding. After making an estimate of salivary flow it was concluded that there is an inflow of water across the ruminal wall while the ruminal liquor is hyperosmolar and also while it is hyposmolar with respect to serum. The relationship of the post-prandial flow of water into the rumen from the extracellular fluid is discussed in relation to primary ruminal tympany.