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-)

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In our previous report2), it was proposed that some quantitative informations concerning the transference of NH3-N in the rumen can be known by the use of kinetic method after the administration of 15N labeled substances. In the present report, 15N-urea has been given to a cow for the purpose of the further confirmation of that possibility, and of finding out the degree of the utilization of urea-N by rumen microbes.In the present experiment (exp. III), 49.9g of 5.786 atom-% excess 15N-urea (N: 41.3%) and 223.6g of polyethylenglycol-4, 000 (PEG) were administered orally at the same time to the animal weighing 591kg, which had been maintained on such a ration as shown in table 1, and samples of rumen liquor were taken through the fistula with the lapse of time after the administration. The method of collecting bacteria and protozoa purely from rumen liquor is shown in Fig. 1. In table 2, 15N atom-% excess of bacteria-N, of protozoa-N, and of NH3-N, concentrations of NH3-N and PEG in the rumen, and excess amounts of NH3-15N per 100ml of rumen liquor are listed.As shown in Fig. 1, semi-log plots of the concentrations of PEG in rumen liquor are nearly on a straight line except the one measured at once after the feeding. This means that the volume of liquid in the rumen was kept nearly constant. Furthermore, the amounts of proteinN per unit volume of rumen liquor were also found to be nearly constant from one feeding time to the next except immediately after the feeding (Table 3). These observations are considered to show that the compartments, A, B, and P in Fig. 4 might be held in the steady state enough to be able to deal with mathematically.In the scheme shown as Fig. 4, k6 means the decreasing rate of NH3-15N that is caused by flowing out toward the omasum, and it can be equal to that of PEG which is calculated as 0.124h-1 from Fig. 2. The net decreasing rate K(=kl+k5+k6) of NH3-15N in compartment A can be obtained as 0.864h-1 from the linear part of Fig. 3, in which excess amounts of NH315N per 100ml of rumen liquor are semi-log plotted. The value of k1, which means the decreasing rate of NH3-15N through being utilized by bacteria, can be obtained as 0.463h-1 from the analysis of the changes of 15N atom-% excess of bacteria-N (Fig. 5), as discussed in our previous report2)On the basis of these k1, k6, and K values, the following speculation can be made as for the degree of the utilization of urea: Since the turnover time of NH3-15N in the compartment A is 1/K hours, and the rate of utilization of NH3-15N by bacteria is k1 per an hour, the percentage of NH3-15N utilized by bacteria can be obtained from k1×1/K×100, and this value, 53.6%, is considered to mean the degree of urea-N utilized by rumen bacteria in the present experiment. The percentage of NH3-15N flowing out toward the omasum without either being utilized by bacteria or being absorbed through the rumen wall, is obtained as 14.5% from the expression of kg×1/K×100. The rest, ca.30% of urea-N is considered to be absorbed as NH3 through the rumen wall.On establishing the scheme, the possible re-entrance of absorbed 15N into the rumen was neglected, but it has been observed in this experiment. With the existence of such a pathway, the degree of urea utilization by bacteria might be slightly more than 53.6%. When 15N atom-% excess of bacteria-N measured dung full experimental period are plotted on the semi-log coordinate (Fig. 6), the decreasing part of the curve is expressed as a broken line. This can not be explained by the scheme, but may possibly be attributed to the re-cycling of 15N.
社団法人日本畜産学会の論文

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-)

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