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Digesta Passage Measured by Markers in Dairy Cows Fed Two Ratios of Corn Silage:Grain with 0 or 1.2% Sodium Bicarbonate¹

Department of Dairy and Animal Science, The Pennsylvania State University and US Dairy Forage Research Center (Pa Cluster) and US Regional Pasture Research Laboratory, University Park 16802

ABSTRACT

Four multiparous Holstein cows in midlactation fitted with rumen cannulae were in a 4 x 4 Latin square experiment to examine effects of two ratios of corn silage:grain (50:50 or 75:25) and sodium bicarbonate (0 or 1.2% of ration dry matter) on rate of passage of digesta. Marker techniques and mathematical equations were compared. Markers for liquid phase were polyethylene glycol and cobalt-ethylendiaminetetraacetic acid and for particulate phase were lanthanum, samarium, cerium, and chromium-mordanted fiber. A single compartment model was used to measure rate of passage of liquid from concentration of the two markers in ruminal fluid samples. Two two-compartment mathematical models were used to calculate rates of passage of liquid, grain, and fiber from fecal marker concentration. Ruminal liquid volume, rate of flow, and fractional rate of passage were not affected by sodium bicarbonate but increased with greater silage feeding. Ruminal grain and fiber passage were increased when more corn silage was fed. Effects of sodium bicarbonate on ruminal grain and fiber passage were variable, although fiber passage tended to be slowed. Overall, liquid passage exceeded grain passage, which exceeded fiber passage from the rumen. In the total tract, retention time of liquid, grain, and fiber was less when diets contained 75% corn silage. The effect of sodium bicarbonate on retention time of liquid, grain, and fiber in the total tract was variable. Markers and mathematical calculations caused differences in estimates of rate of passage and interpretation of results.

¹ Authorized for publication as Paper No. 6565 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Southern States Cooperative, P.O. Box 26234, Richmond, VA 23260.

³ Eastman Chemical Products, Inc., Technical Service and Develop. Div., Kingsport, TN 37662.

⁴ US Dairy Forage Research Center (Pa Cluster), US Regional Pasture Research Laboratory, University Park, PA 16802.