Peltekova V D, Broderick G A
Agricultural Research Service, USDA, US Dairy Forage Research Center, Madison, WI 53706, USA.
J Dairy Sci. 1996 Apr;79(4):612-9. doi: 10.3168/jds.S0022-0302(96)76406-8.
Net release of degraded N as NH3 and total AA plus microbial protein synthesis, quantified from incorporation of 15NH3 into microbial protein, was used to estimate the rate and extent of in vitro degradation of protein fractions isolated from alfalfa hay and silage. Seven proteins (casein, alfalfa hay, alfalfa silage, extracts from alfalfa hay and silage, and residues from alfalfa hay and silage) were studied. Results from (NH4)2SO4 and SDS-PAGE fractionations suggested that soluble proteins in alfalfa hay and silage differed in susceptibility to proteolytic attack. Although the net release of NH3 plus total AA N from alfalfa silage and alfalfa silage extract was twofold greater than that from alfalfa hay and alfalfa hay extract, net microbial protein synthesis on alfalfa hay and alfalfa hay extract was 33 and 43% greater. Despite greater NPN content in alfalfa silage, protein degradation rate and estimated escape were similar for intact alfalfa hay (0.103/h and 43%) and silage (0.067/h and 43%). This result might be explained by the less efficient microbial utilization of silage NPN, greater protozoal numbers on hay, greater soluble true protein in hay, or differences in molecular mass and stability of soluble proteins in hay versus silage. Use of a two-compartment model, based on water-soluble and insoluble CP fractions assumed to pass with the liquid and solid phases, respectively, yielded RUP estimates for alfalfa hay and silage that were similar to NRC estimates.
以氨（NH₃）形式释放的降解态氮以及总氨基酸加上微生物蛋白质合成（通过¹⁵NH₃掺入微生物蛋白质来定量），被用于估计从苜蓿干草和青贮饲料中分离出的蛋白质组分的体外降解速率和程度。研究了七种蛋白质（酪蛋白、苜蓿干草、苜蓿青贮饲料、苜蓿干草和青贮饲料的提取物以及苜蓿干草和青贮饲料的残渣）。硫酸铵（(NH₄)₂SO₄）分级分离和十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳（SDS - PAGE）分级分离的结果表明，苜蓿干草和青贮饲料中的可溶性蛋白质对蛋白水解攻击的敏感性不同。尽管苜蓿青贮饲料及其提取物中氨加上总氨基酸氮的净释放量比苜蓿干草及其提取物高出两倍，但苜蓿干草及其提取物上的微生物蛋白质净合成量分别高出33%和43%。尽管苜蓿青贮饲料中的非蛋白氮（NPN）含量更高，但完整苜蓿干草（0.103/h和43%）和青贮饲料（0.067/h和43%）的蛋白质降解率和估计的逃逸率相似。这一结果可能是由于青贮饲料NPN的微生物利用效率较低、干草上原生动物数量较多、干草中可溶性真蛋白含量较高，或者是干草与青贮饲料中可溶性蛋白质的分子量和稳定性存在差异。基于分别假定随液相和固相通过的水溶性和不溶性粗蛋白组分的两室模型，得出的苜蓿干草和青贮饲料的瘤胃未降解蛋白（RUP）估计值与美国国家研究委员会（NRC）的估计值相似。
