反芻胃内におけるアンモニア態窒素の動態に関する動力学的考察 (反芻動物における非蛋白態窒素化合物の利用-1,2-)

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概要

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• Althougt the non-protein nitrogenous compounds (NPN-compds.) such as urea and ammonium salts are known to be utilized as protein substitutes in ruminants, many of quantitative aspects concerning their utilization have not been elucidated. It has become more important than ever to determine (a) the degree of NH3 fixed by rumen microorganisms, (b) the quantitative role played by each of bacteria and protozoa, and (c) the relative significance of rumen microorganisms in the net utilization of NPN-compds. These problems have hardly been subjected to an in vivo experimental test, because of the complexity of dinamic states of various N-components in the rumen, as well as of the difficulty of definite seperation among such components. But as for the metabolic pathways of NPN in the rumen, many informations have been accumulated since a few decades, and some N-components including bacteria and protozoa can be drawn, if partially, without any appreciable contamination. Under these circumstances, with the use of NPN-compds. labeled with 15N, a new kinetic approach appears to become available to throw light upon the problems mentioned above.In order to make it possible to deal mathematically with the transference of 15N in the rumen, it is necessary to establish the simplest scheme possible about it. In this sense the scheme established in this paper (Fig. 1) is deboid of the possible re-entrance of absorbed 15N into the rumen through such a pathway as so-called "recycling of urea". Furthermore, the appearance of 15N into the protozoa-N pool is defined to be conducted only by way of bacteria, and any other pathway, if possible, is negrected. For the mathematical treatment of this scheme, it must be premised that each compartment in Fig. 1 (A, B and P) is held in the steady state. Such a steady state is assumed to be held at least under a regular feeding condition. On this premise the equations (9) and (11) could be obtained to express the changes of 15N atom-% excess in bacteria and protozoa, respectively.The equation (9) shows that the curve for 15N atom-% excess of bacteria-N is decomposed into two straight lines when they are plotted on the semi-log coordinate. Applying this information to the results of our former experiments1), in which 15N-ammoniumcitrate (exp. I) and 15Nurea (exp. II) were administered independently to a cow, the following values were obtained for three unknowns in equation (9): A0'=0.610 atom-% excess, k1=0.463h-1, and r=0.064h-1 in exp. II (Fig. 2), and A0'=0.640 atom-% excess, k1=0.451h-1, and r=0.063h-1 in exp. I (Fig. 3). k1 means the decreasing rate of NH3-15N that is caused by being utilized by bacteria per an hour, and the values obtained here indicate that the velocity of the utilization of NH3-N by rumen bacteria is 45-46% per an hour. On the other hand, the velocity of the ingestion of bacteria-N by protozoa seems to be less than 6% per an hour, for r(=k2+k3) means the decreasing rate of bacteria-15N that is caused by flowing out toward the omasum as well as being ingested by protozoa. These velocities, however, do not necessarily mean the degrees of N conversions, because turnover times of 15N in compartments A and B must also be taken into consideration.In order to obtain further informations about quantitative problems, it is essential to know all of the k values in Fig. 1, and a new experiment is accordingly now in progress in our laboratory.

• 公益社団法人 日本畜産学会の論文

著者

• 阿部 又信

  東京大学農学部

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• 反芻胃内微生物による尿素態窒素の利用性 (反芻動物における非蛋白態窒素化合物の利用-1,2-)
• 反芻胃内におけるアンモニア態窒素の動態に関する動力学的考察 (反芻動物における非蛋白態窒素化合物の利用-1,2-)

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