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Effect of Level of Forage Intake on Rumen Ammonia, pH, Liquid Volume and Liquid Dilution Rate in Beef Cattle¹

US Department of Agricultural and Montana Agricultural Experiment Station, Cooperating, Miles City, MT 59301

Abstract

Five ruminal-cannulated steers were assigned to a 5 x 5 Latin square design to determine the effects of forage intake on 24-h rumen ammonia N patterns, liquid volume and liquid dilution rate. Sums of squares were partitioned into linear, quadratic and cubic components. Treatments consisted of alfalfa hay fed once daily at 1.40, 1.65, 1.90, 2.15 and 2.40% of body weight. Samples of rumen fluid were taken immediately before feeding and at 2, 4, 8, 12, 16 and 24 h postfeeding; Cr-ethylene-diaminetetraacetic acid (CrEDTA) was used as a marker to estimate rumen liquid volume and liquid dilution rate. A linear relationship (P<.01) occurred between rumen pH and ammonia N concentrations. The effects of pH on rumen ammonia N concentrations were attributed to time after feeding but not treatment. Rumen ammonia N concentrations preand postfeeding reflected differences in forage intake, but relationships varied with respect to time after feeding. Concentrations (mg/100 ml) of rumen ammonia N adjusted for rumen pH were 19.6, 22.2, 22.0, 22.0 and 27.5 immediately before feeding and 41.5, 43.0, 39.1, 40.6 and 34.6 at 2 h postfeeding for forage levels 1.40 through 2.40, respectively. Liquid dilution rates (%/h) ranged from 4.3 to 7.2 and increased linearly .6% with each .25% increase in forage intake per unit of body weight. Rumen liquid volumes were 149.3, 129.8, 137.0, 135.1 and 99.5 liters for steers fed forage levels 1.40 through 2.40, respectively.

¹ This study was conducted at the Livestock and Range Res. Sta., Miles City, MT, as a contribution to Western Regional Project W-151. Publication has been approved by the Director of the Montana Agr. Exp. Sta., as Journal Series No. 1329.