The utilization of urea in the bovine rumen. 3. The synthesis and breakdown of protein in rumen ingesta.

1. In the utilization of urea by dairy cattle the first stage is probably the conversion of urea to NH3 in the rumen. Moreover, the urease activity of the rumen ingesta is so great at all times of the day, whatever the time of feeding, and remains so little affected by relatively large apaounts of urea, that all the urea ever likely to be fed, even to a high yielding cow in full lactation, would readily be converted to NH3 within 1 hr. This fact has been confirmed by Wegner, Booth, Bohstedt & Hart [1941], who found a marked increase in N.P.N. and NH3 in the rumen after a urea meal but were unable to detect urea itself. 2. The urease of the rumen resembles, in activity, that from soya and jack beans. Changes in its activity with changes in temperature and pH, and its behaviour in the presence of such inhibitors as quinone and NaF, are typical of enzymes of the urease type. Preliminary attempts to obtain enzyme preparations free from bacteria have, however, proved unsuccessful.