Influences of diet, short-chain fatty acids, lactate and chloride on bicarbonate movement across the reticulo-rumen wall of sheep

Influences of short-chain fatty acids (SCFA), chloride or lactate on net bicarbonate movement were determined in the temporarily isolated and washed reticulo-rumen of sheep used to 100% hay or 81% concentrate diets. Replacement of SCFA by gluconate and mannitol reversed net bicarbonate secretion into net absorption. The reversal of net bicarbonate movement could not be prevented by presence of D/L-lactate. Replacement of chloride in addition to replacement of SCFA enhanced net absorption of bicarbonate. Feeding concentrate diets resulted in an elevation of net bicarbonate secretion and of net SCFA absorption. It is concluded that under the conditions tested net bicarbonate secretion mainly depends on the luminal presence of SCFA. Furthermore, bicarbonate secretion into the reticulo-rumen may be an important factor for alkalizing the rumen contents, especially in sheep adapted to concentrate diets.