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Microbial Species Including Ureolytic Bacteria from the Rumen of Cattle Fed Purified Diets

United States Department of Agriculture, ARS, Animal Husbandry Research Division, Beltsville, Maryland

The rumen microbial populations were studied in cattle fed either natural or purified diets. The purified diets contained either isolated soy protein or 1 of 4 nonprotein nitrogen (NPN) sources. Four-hundred and three strains of bacteria isolated at random from a nonselective medium (264 strains) and a lactobacillus medium (139 strains) were presumptively identified and tested for urease activity. There were 28 and 2 ureolytic strains among the total bacteria isolated from the nonselective and lactobacillus medium, respectively. The ureolytic strains represented a wide variety of bacteria. Among the total population, the most predominant presumptively identified groups of bacteria grown on nonselective medium were anaerobic lactobacilli and Bacteroides amylophilus. The latter group's concentrations in rumen contents were higher in the steers fed either urea or urea phosphate than in steers fed biuret or uric acid. The percentage of facultative anaerobic and H₂S-producing ruminal bacteria were significantly greater for steers fed biruet than for steers fed the other NPN sources. Steers fed uric acid had significantly more cellulolytic bacteria than steers fed urea and urea phosphate and steers fed urea had significantly more amylolytic bacteria than steers fed urea phosphate. Cattle fed a 30% roughage-70% concentrate natural diet contained significantly more ruminal protozoa and gramnegative rod-shaped bacteria but contained significantly fewer cocci than cattle fed urea or isolated soy supplemented purified diets.