Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 1996
Publication Date: N/A
Technical Abstract: Evidence suggests that during ruminal adaptation to high levels of nitrate (NO3), nonfermentative, respiratory NO3 and nitrite (NO2) reducing bacteria increase in number due to selective pressure of NO3/NO2. In this experiment, we characterized changes occurring between populations of strict NO3 reducing bacteria and those having fermentative capability. Three goats were fed an alfalfa:corn (9:1) diet supplemented with increasing amounts of NaNO3, culminating with a dose of 180 mg NaNO3/kg body wt per d. Rates of NO3 and NO2 reduction by microbes in rumen contents from unadapted goats were 0.36 +/- 0.1 and 0.45 +/- 0.1 umol/ml/h, respectively. The rate of NO3, but not NO2, reduction was increased 2- to 3-fold following adaptation. Numbers of bacteria were also estimated and we report log transformations of most probable number calculations (bacteria/g rumen contents). Combined, the number of fermentative and respiratory NO3 reducing bacteria in rumen contents increased from 7.6 +/- 0.3 to 8.7 +/- 0.8 following adaptation. Using a selective medium, we found that the number of respiratory NO3 reducing bacteria in rumen contents increased from 7.6 +/- 0.3 to 8.1 +/- 0.1 following adaptation. Thus, while strict NO3 respiring bacteria made up a considerable portion of the combined population of NO3 reducing bacteria, the increase during adaptation was due mainly to bacteria from the fermentative group. But, the extent each group contributes to detoxification will also depend on the specific activity of NO3 and NO2 reduction by these bacteria groups.