Changes in ruminal concentrations of microbial ammonia and amino acids due to monensin and time

The effect of monensin (33 mg/kg) and no monensin on distribution of ammonia and free amino acids in fluid and particulate phases of ruminal contents was studied. Two Jersey cows and two Angus-Hereford steers, weighing approximately 350 kg and each containing a ruminal cannula were meal fed a 65% concentrate diet for two periods. Feed was available for 30 min; any feed not eaten was removed after this time. Whole ruminal contents were sampled before feeding, immediately after feed removal and 1, 2, 3, 4, 6, 8, 10 and 12 h after feed removal. A crossover design with split-plot in time was used with four observations per time point per treatment. Extracellular (E) ammonia and amino acids were determined on high speed supernatants of strained ruminal fluid. Total (T) ammonia and amino acids were obtained by lysing microbial cells with 1% cetyltrimethylammonium bromide (CTAB) and one freeze treatment before centrifugation. Intracellular (I) amino acids and ammonia were determined as T minus E. Squeezed particles were suspended in .1 N HCl containing 1% CTAB. Total and E ammonia were higher throughout the study for no monensin vs monensin (P less than .05). Intracellular ammonia was low (.03 to 1 mM) and did not change (P greater than .10) across time for either dietary treatment. Intracellular amino acids ranged from 1.2 to 4.5 mM and were higher (P less than .05) than E amino acids (.9 to 2.2 mM) for both diets immediately after feeding. Monensin did not significantly lower (P greater than .10) T amino acids compared with no monensin throughout sampling (2.6 and 3.1 mM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)