Saliva secretion and its relation to feeding in cattle

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Abstract
In cows with a permanent rumen fistula the rate of secretion of mixed saliva during eating was estimated by drying boluses of various foods collected at the cardia. The mean rate of secretion was 229 ml/min, which was 2 to 4 times greater than the rate of secretion of mixed saliva during rest. The amount of saliva added to a given weight of food varied greatly with different foods. The variations were due partly to differences in the rate of secretion of saliva with different foods, but mainly to differences in the rate at which the foods were eaten, the more fibrous foods being eaten more slowly than the less fibrous. These differences in the rate of eating were due primarily to differences in the size of the boluses, with smaller effects due to differences in the rate at which the boluses were swallowed. Fluid squeezed from swallowed boluses of dairy cubes and 2 kinds of hay had a greater tonicity and higher concentration of certain inorganic ions than did mixed saliva secreted during rest. This finding suggested that ensalivation during mastication was effective in bringing soluble food constituents into solution. Removal of the contents of the mouth during rumination suggested that up to 50% of the regurgitated solid material may escape re-mastication and be re-swallowed without further ensalivation. It is postulated that the increased flow of parotid saliva during rumination serves to wash the re-masticated digesta, from the space between cheek and teeth, into the esophagus. Tentative estimates suggest that the total daily secretion of mixed saliva in 4 cows varied from 98 to 190 1 with 5 different diets.