The assimilation of ammonia nitrogen by bacteria of the rumen of sheep

McDonald (1952) discussed the role of ammonia in the rumen and pointed out that many kinds of bacteria are not fastidious in their nitrogen requirements, and that in the rumen growth of bacteria that use ammonia as a source of N is to be expected.Much work has been done on the use of non-protein N, especially of urea, in the feeding of ruminants, and there is now no doubt that the N of many simple nitrogenous compounds can be incorporated in bacterial protein and so be of value to the animal.The work of Pearson & Smith (1943) showed that, in incubated rumen liquor, urea was rapidly hydrolysed to ammonia, and provided evidence that protein was being formed from ammonia by the rumen bacteria.The ability of rumen bacteria to grow with ammonia as their sole or part source of N has not been closely investigated, and although organisms have been classified according to their ability to ferment carbohydrates or to deaminate amino acids, their ability to assimilate ammonia-N has only recently received attention, in particular from Bryant (1961).The fact that the addition of starch to a protein-rich diet depressed the concentration of ammonia present in the rumen (McDonald, 1952; Chalmers & Synge, 1954;Annison, Chalmers, Marshall & Synge, 1954) suggested that starch-fermenting bacteria in particular might possess the property of using ammonia-N for growth.The experiments described here were undertaken to find whether it were so.