Estimating salivary flow and ruminal water balance of intake, diet, feeding pattern, and slaframine

Three experiments with ruminally fistulated cattle fed 12 times daily were conducted to study the role of saliva secretion in ruminal water balance when intake, diet, and feeding pattern were altered. Water balance data were determined from continuously infused Co-EDTA and pulse-dosed Cr-EDTA with saliva flow estimated by difference between water intake and ruminal outflow. Any net transruminal water flux would be included in the estimate of salivary flow. When the concentration of bluestem hay in the diet was increased from 50 to 90%, ruminal fluid volume, saliva secretion, water intake, dilution rate, and total ruminal outflow increased. At equal intake, the higher forage diet increased ruminal liquid volume, outflow, and saliva secretion but had no effect on dilution rate. Intake, but not forage concentration, affected ruminal pH when 50 and 90% hay diets were fed. Increasing feeding frequency of forage in a 65% bluestem hay diet from 4 to 12 times daily (the grain portion was fed 12 times daily) increased dilution and ruminal outflow; however, the latter was only significant with data from Cr-EDTA. Ruminal volatile fatty acids were not altered by feeding frequency of forage. Nycterohemeral patterns were seen in water intake, ruminal dilution rate, outflow, and salivary flow in both studies. Slaframine increased saliva flow by 29% and was accompanied by increased ruminal liquid volume, dilution rate, and outflow.