Diurnal Variation in Rumen Volume and Metabolite Concentrations

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Abstract
Average volumes of whole rumen con- tents were 3.33, 2.83, 3.38, and 3.47 liters for )0 wethers with free access to water and 2.87, 2.64, 3.13, and 3.23 for 10 weth- ers deprived of water 4, 8, 12, and 24 hours post-prandial. The rate of 144Ce dilution for fluid flow into the rumen was inversely proportional to time post-feeding (~ == 38.61 -- 12.546 In x). Actual flow of con- tents out of the rumen for 4 to 8, 8 to 12, and 12 to 24 hours after feeding were 730, 170, and 85 ml per hour for wethers given water and 490, )50, and 120 ml per hour for those without water. Total rumen dry matter (~) decreased linearly with time (x) when both variables were plotted as logarithms base e according to the regres- sion equation ~, : 985x -°-33s. Rumen vola- tile fatty acids were higher 4 and 8 hours after feeding in sheep deprived of water than in those with free access to water. Respective regression equations were ~ = 19.5e -°.°a4x and S' = 26-0e-°'°4°x for sheep with and without water. In vitro gas pro- duction rate of whole rumen contents de- creased with time post-feeding. Gas pro- duction rate was not significantly affected by treatment when the data were expressed as milliliters of gas produced per min- ute for the total rumen mass. A semilog plot of total gas production rate fit a straight line and a regression equation ~ = 58.3e -°.°431x. Total rumen deoxyribo- nucleic acid was not affected by treatment or sampling time.