Modification Of The Methods In ¹⁵N Tracer And Their Use In Determination Of Rumen Microbial Protein Synthesis

This thesis was composed of all the results from three experiments (which)were conducted to improve ZHT-03 mass spectrometer(MS), and the calculation methods for ¹⁵N tracer, and to investigate the efficiency of urea to rumen microbial protein and its distribution in rumen digesta using ¹⁵N in vitro.Experiment 1 The system of scanning control and data acquisition for ZHT-03 MSThe automatic scanning control and the data acquisition were achieved after improving the circuit of ZHT-03 mass spectrometer and using the cards of data acquisition and application software 16 bit A/D was used in analog-to-digital conversion. The results of 4 standard samples of ¹⁵N% from 0.366% to 5.264% indicated that the accuracy and precision of the results were enhanced significantly after the instrument improved, and the precision were all over the 99.80%. The real data, diagram, analytical state and results were displayed dynamically and all the information of samples were stored as Excel format. As a result, the performance and the degree of automation of mass spectrometer were improved greatly.Experiment 2 Improvements of calculation methods in ¹⁵N tracer researchBased on the change of ¹⁵N abundance can lead to the change of atomic weight of nitrogen , the effects of ¹⁵N abundance on the quantity of tracer, total nitrogen content and Ndff were analyzed in accordance with the theory of chemistry and isotope dilution. The calculation methods with the mol rather than weight as the unit of nitrogen were proposed. Thus the error caused by calculation methods per se could be eliminated and the accuracy and reliability of the results be increased.Experiment 3 Studies on the efficiency of urea to rumen microbe protein using ¹⁵N in vitroA completely randomized design involving 4×2 factorial arrangement of treatments was used to investigate the efficiency of urea to rumen microbe protein in vitro. There were all together four urea levels: urea replaced diet CP of 0, 10%, 20%, 40%, and two fermentation time: 24 h and 48 h for the treatments. The results showed that the ratio of diet CP replaced by urea had no significant effect on supernatant fluid (SF) pH, NH3 concentration and undigested feed (UDF) dry matter. The pH and NH3–N concentration of SF increased significantly with the fermentation time, UDF dry matter, however, decreased significantly with it. The amount of urea distributed in digesta fractions and the ratio of urea nitrogen to corresponding fractions increased significantly with the ratio of diet CP replaced by urea. The efficiency of urea to rumen microbial protein reached the peak, 53.6%, at 24h with urea replaced diet CP of 10%. The amount of urea distributed in digesta fractions decreased from SF, UDF, liquid - associated microbe to particle - associated microbe.