Effect of sampling location, time, and method of concentration of ammonia nitrogen in rumen fluid.

In experiment 1, rumen fluid samples were obtained from dorsal, midpoint, and ventral regions of the rumen of rumenfistulated dairy cows at hourly intervals for 24 h. Dorsal, midpoint, and ventral rumen fluid samples contained 16.1, 14.2, and 12.1 mg/100 ml of ammonia nitrogen. Time after feeding resulted in differences in the concentration of ammonia in rumen fluid with the greatest concentration 30 to 90 min postfeeding. The concentration of ammonia nitrogen was greater for cows fed a high-concentrate diet (14.7% crude protein, 86% concentrate) than for cows receiving a normal diet (15.1% crude protein, 42% concentrate), 15.2 versus 13.1 mg/100 ml. In a second experiment, rumen fluid samples were obtained immediately before feeding and at 1 and 6 h postfeeding by stomach tube and from dorsal, midpoint, ventral, and mixed rumen contents via a rumen cannula. Concentrations of ammonia nitrogen (mg/100 ml) in the respective rumen fluid samples were 14.3, 23.0, 18.3, 17.2, and 19.6. Location of sampling, method of sampling, time of sampling, type of diet, and rumen fluid volume are factors that affect the concentration of ammonia nitrogen in rumen fluid.