CHANGES IN AMMONIA CONCENTRATION, BACTERIAL COUNTS, pH AND VOLATILE FATTY ACID CONCENTRATION IN RUMEN OF COWS FED ALFALFA HAY OR CONCENTRATE: UREA-CORN SILAGE

Publisher Website
Google Scholar
Abstract
Four rumen-fistulated cows were fed alfalfa hay (15.4% CP) ad libitum for 4 wk prior to the experiment and from day 1 to day 8 of the experiment. From days 9 to 15 (period 2) and from days 16 to 39 (period 3) they were fed ad libitum concentrate: urea-corn silage (15.9% CP). Rumen fluid samples were collected from 0600 to 1600 h during the three periods and changes in the pH, concentrations of ammonia and volatile fatty acids (VFA) and bacterial counts were determined. Ammonia, pH and VFA concentrations showed oscillatory behavior even on an ad libitum feeding schedule. Rates of production and utilization of ammonia were significantly higher with the concentrate: urea-corn silage diet than with the hay diet. VFA concentration and pH were inversely related. Periods of high VFA production coincided with periods of rapid ammonia utilization. The evidence indicated that there was a metabolic adaptation in the rumen for better utilization of ammonia. Concentrations of amino acids and peptides were nearly 1 mM in the rumen fluid throughout the day and increased to 3 mM immediately after feeding. Most of the increases were due to alanine, leucine and aspartic acid. It is concluded that the practice in nutritional studies of measuring and reporting rumen ammonia, VFA and pH only once at one time point in an experiment or even the mean of several determinations does not adequately represent the complex metabolic changes in the rumen. Key words: rumen, ammonia, fermentation, pH, adaptation, amino acids