Influence of saline drinking water on the flow and mineral composition of saliva and rumen fluid of sheep

Abstract

The influence of sodium chloride ingestion via the drinking water upon the flux of fluid and minerals to and from the rumen of sheep has been examined. Four Merino wethers were each prepared with ruminal and bilateral parotid duct fistulas to allow continuous sampling and measurement of flow rates and were offered rainwater which was zero, 136 or 221mM with respect to sodium chloride as the only source of drinking fluid.

Parotid salivary flow rate decreased by up to 43% when the saline concentration of the drinking water was increased. There was an inverse relationship between saliva flow rate and the fluid intake, but much of the effect appeared to be due to ingestion of sodium chloride per se. Salt water ingestion caused an increase in the salivary concentration of sodium and phosphate; a decrease in that of potassium; and no change in that of chloride or osmolality. The rate of secretion of sodium varied directly with saliva flow rate.

The outflow of water from the rumen to the omasum, or its net absorption across the rumen wall, were not influenced by treatment. In centrifuged rumen fluid samples saline ingestion caused increased levels of sodium, chloride and osmolality; decreased levels of potassium; and no change in calcium, magnesium or phosphate. Outflows of sodium and chloride to the omasum were increased.

The apparent absorption of sodium and chloride from the rumen increased proportionately to the inflows of these ions via the saliva and drinking fluid. The additional sodium and chloride ions arising from the ingested saline were absorbed in approximately equal amounts.

Saline drinking by sheep leads to a reduction in the rate of secretion of parotid saliva and its accompanying ions, which partially compensates for the added amount of fluid and electrolyte which enter the rumen in the drinking water.