The effects of dehydration on electrolyte concentrations and water content along the large intestine of a small ruminant: The Dik-dik antelope

Abstract

1. The concentrations of Na, K, and Cl and the water content in the large intestine and rectum of an East African ruminant, the Dik-dik antelope, was investigated in hydrated and dehydrated animals. 2. Intestinal contents were removed at six sites along the large intestine and rectum, and the water fraction and the amounts of Na, K, and Cl were measured per g dry matter. An impermeant water marker showed that the dry matter amount was nearly constant along the lower gut. Local electrolyte absorption rates were determined in the terminal colon by a dialysis bag method. 3. Approximately 4/5 of the absorption of NaCl and H2O took place in the upper large intestine. Throughout the lower gut the Na concentration of the absorbate was close to that of plasma. The Na and Cl concentrations of the digesta decreased aborally while the K concentration rose, but K was still absorbed. 4. Dehydration resulted in a reduction of 35% of the water lost per gram dry faeces. The water content was reduced from the start of the large intestine (by 13%), but the fractional absorption of salt and water in the large intestine and rectum was not significantly changed. The local electrolyte absorption rates and the electrical potential difference were slightly reduced. The Na and K concentrations of the absorbate remained nearly constant. The water saving during dehydration thus seems to proceed without specific adjustments of the transport parameters of the lower gut. The concentrations of Na and Cl in faeces approach those which in dialysis bag experiments result in zero absorption rates. This explains the constant fractional absorption of NaCl and water in the lower gut at different flow rates of dry matter. 5. Animals shot in the field were not dehydrated, but more Na-depleted than those studied in captivity. They had a pronounced net K absorption in the lower gut.