Eubacterium limosum was isolated as the most numerous methanol-utilizing bacterium in the rumen fluid of sheep fed a diet in which molasses was a major component (mean most probable number of 6.3 x 108 viable cells per ml). It was also isolated from sewage sludge at 9.5 x 104 cells per ml. It was not detected in the rumen fluid of a steer on a normal hay-grain diet, although Methanosarcina, as expected, was found at 9.5 x 10i cells per ml. The doubling time of E. limosum in basal medium (5% rumen fluid) with methanol as the energy source (370C) was 7 h. Acetate, cysteine, carbon dioxide, and the vitamins biotin, calcium-D-pantothenate, and lipoic acid were required for growth on a chemically defined methanol medium. Acetate, butyrate, and caproate were produced from methanol. Ammonia or each of several amino acids served as the main nitrogen source. Other energy sources included adonitol, arabitol, erythritol, fructose, glucose, isoleucine, lactate, mannitol, ribose, valine, and H2-CO2. The doubling time for growth on H2-CO2 (5% rumen fluid, 370C) was 14 h as compared with 5.2 h for isoleucine and 3.5 h for glucose. The vitamin requirements for growth on H2-C02 were the same as those for methanol; however, acetate was not required for growth on H2-CO2, although it was necessary for growth on valine, isoleucine, and lactate and was stimulatory to growth on glucose. Acetate and butyrate were formed during growth on H2-CO2, whereas branched-chain fatty acids and ammonia were fermentation products from the amino acids. Heat tolerance was detected, but spores were not observed. The type strain of E. limosum (ATCC 8486) and strain L34, which was isolated from the rumen of a young calf, grew on methanol, H2-CO2, valine, and isoleucine and showed the same requirements for acetate as the freshly isolated strains.

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The ability of mineral salts to alter rumen fermentation, rumen fluid dilution rate, milk fat synthesis, and nutrient utilization was investigated in dairy cows fed a high-concentrate, milk-fat depressing diet. Four rumen-fistulated Holstein cows were in a 4 X 4 Latin square design. Treatments consisted of: 1) basal (25% corn silage: 75% concentrate on a dry matter basis), 2) basal + 2.0% sodium chloride, 3) basal + 2.0% sodium bicarbonate, and 4) basal + 2.4% limestone. Addition of limestone to the basal diet reduced dry matter intake but increased efficiency of dietary nutrient utilization for milk synthesis. Sodium bicarbonate increased synthesis of milk fat. Sodium chloride also tended to increase milk fat synthesis whereas limestone had no effect. Milk yields (kg/day) and milk fat (%) for the four treatments were 1) 29.5, 2.40; 2) 29.3, 2.66; 3) 28.9, 3.26; and 4) 29.2, 2.32. Rumen fluid pH, dilution rate (%/hour), and molar percentage of acetate and propionate were: 1) 5.98, 10.3, 49 and 39; 2) 6.02, 12.4, 55 and 32; 3) 6.16, 12.2, 58 and 25; and 4) 5.92, 10.7, 51 and 38. Limestone was totally ineffective in altering ruminal pH, fluid dilution rate, molar percentages of acetate and propionate, and synthesis of milk fat. Improved feed efficiency for milk production after addition of limestone was related to an increase in starch digestion compared to the basal ration (95 versus 88%).