Broderick Glen A, Murphy Michael L, Udén Peter
Agricultural Research Service, USDA, US Dairy Forage Research Center, Madison, WI 53706, USA.
J Dairy Sci. 2004 May;87(5):1360-71. doi: 10.3168/jds.S0022-0302(04)73285-3.
Effects of varying the concentrations of hydrazine sulfate (HS) and chloramphenicol (CAP), inhibitors of microbial-N uptake and protein synthesis, on rates of protein degradation estimated from net appearance of NH3 and total amino acids (TAA) were studied in a ruminal in vitro fermentation system. Without inhibitors, recoveries of N added as NH3 and TAA were 4 and 6% after 4-h incubations, and apparent degradation rates estimated from release of NH3 and TAA for casein, solvent soybean meal (SSBM), and expeller soybean meal (ESBM) approached 0. Increasing inhibitor concentrations from the standard amounts of 1 mM HS plus 30 mg of CAP/L to 2 mM HS plus 90 mg of CAP/ L gave rise to numerically greater N recoveries and degradation rates, but these differences were not statistically significant. Compared with the standard inhibitor concentrations, use of 2 mM HS, without CAP, yielded similar recoveries and rates, but 30 or 90 mg of CAP/L, without HS, was not satisfactory. Versus that with 1 mM HS plus 30 mg of CAP/L, media containing 2 mM HS plus 90 mg of CAP/L gave increased TAA recoveries and higher rates for casein, but not SSBM, in the presence of added starch. Faster degradation rates were obtained for casein, but slower rates for SSBM and ESBM, in Sweden versus Wisconsin using inocula from cows fed different diets but with similar CP and energy contents. Differences in microbial catabolism of peptides may account for differences in degradation rates observed between Sweden and Wisconsin. Adding NH3 plus free and peptide-bound amino acids to the inoculum reduced apparent degradation rates, possibly via end-product inhibition. Analysis of data from multiple time-point incubations indicated that casein degradation followed simple, first-order kinetics, while a biexponential model fitted degradation patterns for both SSBM and ESBM.
在瘤胃体外发酵系统中，研究了改变硫酸肼（HS）和氯霉素（CAP）（微生物氮吸收和蛋白质合成抑制剂）的浓度对根据氨和总氨基酸（TAA）的净出现量估算的蛋白质降解率的影响。在没有抑制剂的情况下，孵育4小时后，以氨和TAA形式添加的氮的回收率分别为4%和6%，根据酪蛋白、溶剂浸出豆粕（SSBM）和压榨豆粕（ESBM）的氨和TAA释放量估算的表观降解率接近0。将抑制剂浓度从标准量的1 mM HS加30 mg CAP/L增加到2 mM HS加90 mg CAP/L，导致氮回收率和降解率在数值上更高，但这些差异无统计学意义。与标准抑制剂浓度相比，使用2 mM HS（无CAP）产生了相似的回收率和降解率，但30或90 mg CAP/L（无HS）并不理想。与含有1 mM HS加30 mg CAP/L的培养基相比，如果添加淀粉，含有2 mM HS加90 mg CAP/L的培养基可提高酪蛋白的TAA回收率和降解率，但对SSBM则不然。在瑞典与威斯康星州，使用来自饲喂不同日粮但粗蛋白和能量含量相似奶牛的接种物时发现酪蛋白降解率更快，而SSBM和ESBM的降解率较慢。瑞典和威斯康星州之间观察到的降解率差异可能是由于肽的微生物分解代谢不同。向接种物中添加氨以及游离和肽结合氨基酸可降低表观降解率，这可能是通过终产物抑制实现的。对多个时间点孵育数据的分析表明，酪蛋白降解遵循简单的一级动力学，而双指数模型适合SSBM和ESBM的降解模式。
