Cockburn J E, Williams A P
Br J Nutr. 1984 Jan;51(1):111-32. doi: 10.1079/bjn19840014.
Four steers were given straw and tapioca diets, twice daily, in a 4 X 4 Latin-square design. These diets, containing 4.2 g nitrogen/kg dry matter (DM), were further supplemented with either urea, decorticated groundnut meal (DCGM), untreated (UT) casein or formaldehyde-treated (FT) casein to give a total of 19.7 g N/kg DM and 10.5 MJ/kg DM daily. Concurrent samples of rumen bacteria and protozoa and abomasal digesta were collected for each period of the experiment and the concentrations of 2-aminoethyl phosphonic acid (AEPA), diaminopimelic acid (DAPA), total nitrogen (TN), total phosphorus (TP), amino acids and hexosamines were determined in the dried preparations. The nature of the dietary supplements had little effect on the concentrations of most of these constituents or on the total protozoal numbers. Abomasal digesta samples marked with polyethylene glycol (PEG) and chromic oxide for flow estimation were collected over 24 h, and the proportions of protozoal-N, bacterial-N and microbial-N estimated simultaneously using the markers AEPA, DAPA and RNA respectively. These digesta-N components were also estimated using an amino acid profiling (AAP) method which gave, in addition, estimates of the dietary and endogenous components. For the diets containing casein, the proportion of dietary casein was estimated directly using casein-P as a marker. Estimates of the respective mean proportions of microbial-N in abomasal digesta non-ammonia-N (NAN) for the diets containing urea, DCGM, UT casein or FT casein were: AEPA 0.56, 0.32, 0.27 and 0.16; DAPA 0.88, 0.70, 0.81 and 0.57; RNA 0.98, 0.85, 0.92 and 0.53. Giving FT casein significantly (P less than 0.001) increased the flow of casein-N at the abomasum and a significantly (P less than 0.001) greater proportion of casein-N was found in abomasal NAN (0.51 v. 0.09) where FT rather than UT casein was given. The AAP method gave results for the proportions of microbial- and dietary-N (where casein was given) which were, in general, slightly lower than those obtained using RNA and casein-P as markers. Agreement with estimates of bacterial protein (from DAPA) and of protozoal protein (from AEPA) was less satisfactory. Comparisons of the various estimates of the proportions of microbial-N in abomasal digesta suggested that the results obtained for protozoal-N by AEPA were overestimates. AEPA was found in mixed rumen bacteria which may have accounted in part for these overestimates. However, AEPA was not detected in any of the dietary ingredients.
选用4头阉牛，采用4×4拉丁方设计，每天分两次投喂稻草和木薯日粮。这些日粮含氮量为4.2克/千克干物质（DM），再分别添加尿素、去皮花生粕（DCGM）、未处理（UT）酪蛋白或经甲醛处理（FT）的酪蛋白，使日粮总氮含量达到19.7克/千克DM，每天能量达到10.5兆焦/千克DM。在实验的每个阶段，同时采集瘤胃细菌、原虫和皱胃消化物样本，测定干燥样本中2-氨基乙基膦酸（AEPA）、二氨基庚二酸（DAPA）、总氮（TN）、总磷（TP）、氨基酸和己糖胺的浓度。日粮添加物的种类对这些成分中大多数的浓度以及原虫总数影响很小。收集用聚乙二醇（PEG）和氧化铬标记用于流量估算的皱胃消化物样本，时长为24小时，分别使用标记物AEPA、DAPA和RNA同时估算原虫氮、细菌氮和微生物氮的比例。还采用氨基酸谱分析（AAP）方法估算这些消化物氮成分，此外，该方法还能估算日粮和内源性成分。对于含酪蛋白的日粮，直接用酪蛋白磷作为标记物估算日粮酪蛋白的比例。含尿素、DCGM、UT酪蛋白或FT酪蛋白的日粮，皱胃消化物非氨氮（NAN）中微生物氮各自的平均比例估算值如下：AEPA法分别为0.56、0.32、0.27和0.16；DAPA法分别为0.88、0.70、0.81和0.57；RNA法分别为0.98、0.85、0.92和0.53。饲喂FT酪蛋白显著（P＜0.001）增加了皱胃中酪蛋白氮的流量，并且发现饲喂FT酪蛋白时，皱胃NAN中酪蛋白氮的比例显著（P＜0.001）更高（0.51对0.09），而不是UT酪蛋白。AAP方法得出的微生物氮和日粮氮（饲喂酪蛋白时）比例结果，总体上略低于使用RNA和酪蛋白磷作为标记物得出的结果。与细菌蛋白（来自DAPA）和原虫蛋白（来自AEPA）估算值的一致性较差。对皱胃消化物中微生物氮比例的各种估算结果进行比较表明，AEPA法得出的原虫氮结果偏高。在混合瘤胃细菌中发现了AEPA，这可能是造成这些偏高结果的部分原因。然而，在任何日粮成分中均未检测到AEPA。
