In vitro studies on the effect of diet and mucosal PH on ammonia, sodium and chloride transport across the rumen epithelium of sheep

الملخص EN

-This studywas designed to investigate the possible functional adapt-ation of the rumen epithelium to concentrate feeding and to the accompany-ing decrease in the pH of rumen liquor.

Concentrate feeding resulted in stimulation of net Na+ flux rate, ammonia absorption and conductance (Gt), and a reduction of short-circuit current (Isc) and potential difference (PDt) across the isolated rumen epithelium of sheep.

Mucosal disappearance rates of total ammonia were higher than the serosal appearance rates in both hay-and concentrate-fed sheep, indicating ammonia metabolism by the rumen epithelium.

However, the intraepithelial metabolic rate of ammonia was higher in concentrate-fed sheep.

These results support the previous reports on the dietary functional adaptation of sheep rumen epithelium.

Decreasing the mucosal pH from 7.4 to 6.4 resulted in a stimulation of Na+ and Cl- net flux rates, and a reduction of ammonia absorption.

These effects could be attributed to the changes in the dissociation equilibrium (Henderson-Hasselbalch equation) of short chain fatty acids, bicarbonate and ammonia, and their consequent effects on Na+/H+-exchange, Cl-/HCO3--exchange and passive ammonia diffusion, respectively.

It is concluded that rumen epithelium could develop some sort of functional adaptation beside thewell knownmorphological adaptation to concentrate feeding.