Effects of osmolality on water, electrolytes and VFAs absorption from the isolated ruminoreticulum in the cow

Effect of the osmolality on the absorption of water, electrolyte and VFAs from the isolated ruminoreticulum under normal feeding condition were investigated in a series of the study to evaluate the rumen as a potential site of absorption in oral fluid therapy of adult cattle. Thirty of 40 l of the test solutions with varying osmotic pressure (100, 200, 300 and 500 mosmol/L, pH 6.8) were prepared using different concentrations of electrolytes and VFAs. These were infused into the isolated and emptied ruminoreticulum, and the absorption rate of water and each components were studied for 3 hrs. Marked absorption of water was observed with solutions more hypotonic than rumen fluid, the extent of which was more extensive with less osmotic pressure; the absorption rate as high as 47.6% was obtained with a solution 100 mosmol in osmotic pressure. When hypertonic solution (500 mosmol/L) was infused, however, water was transported on the contrary from the blood to the rumen. Absorption rates of electrolytes such as Na, K and Cl were increased according to the elevation of osmolalities and their concentrations in the test solutions. VFAs were also absorbed in large quantities (23.9-74.5%) in any test solutions, though the absorption rates were significantly decreased with the elevation of osmolalities. These results may indicate that the ruminal wall has a high absorptive function for water, electrolytes and VFAs when the osmolalities and the concentration of solutes in the ruminal fluid are maintained within a certain range. Furthermore, it is thought that they may work as a rational support for a possible oral fluid therapy even in adult cows.