Kohn R A, Allen M S
Department of Animal Science, Michigan State University, East Lansing 48824, USA.
J Dairy Sci. 1995 Jul;78(7):1544-51. doi: 10.3168/jds.S0022-0302(95)76776-5.
The influence of maturity and method of conservation on protein degradation was determined for four different forage species. Alfalfa, smooth bromegrass, and reed canarygrass were harvested at three maturities, and whole plant corn was harvested at two maturities. Samples of each forage were freeze-dried or wilted and then ensiled in mini silos at two DM contents. Additional samples of all forages except corn were field-dried to hay. Ground sample was incubated for 0, 2, and 24 h with crude enzyme extract from ruminal contents. Degraded protein as a percentage of total CP was determined as the amount of protein that was soluble in TCA (80 g/L) after degradation. Increased maturity resulted in lower protein degradation for alfalfa, bromegrass, and canarygrass. For example, the most mature alfalfa or bromegrass, respectively, had 77 or 63% as much N that was soluble in TCA after 2 h of incubation with ruminal enzyme than the least mature forage of the same species. Although protein degradation was higher for ensiled than for dried forage, silage DM content had no consistent effect. Freeze-dried material generally had less degraded protein than hay, but protein degradation of bromegrass at 24 h was lower for hay than for freeze-dried samples. Protein degradation of forages was highly variable and depended on plant maturity and conservation method.
测定了成熟度和保存方法对四种不同饲草蛋白质降解的影响。紫花苜蓿、无芒雀麦和披碱草在三个成熟阶段进行收割，全株玉米在两个成熟阶段进行收割。每种饲草样本进行冷冻干燥或萎蔫处理，然后以两种干物质含量装入小型青贮窖青贮。除玉米外的所有饲草的其他样本进行田间干燥制成干草。将粉碎后的样本与瘤胃液粗酶提取物一起孵育0、2和24小时。将降解蛋白占总粗蛋白的百分比确定为降解后可溶于三氯乙酸（80 g/L）的蛋白量。成熟度增加导致紫花苜蓿、雀麦和披碱草的蛋白质降解率降低。例如，最成熟的紫花苜蓿或雀麦在与瘤胃酶孵育2小时后，可溶于三氯乙酸的氮分别是同一物种最不成熟饲草的77%或63%。尽管青贮饲草的蛋白质降解率高于干草，但青贮干物质含量没有一致的影响。冷冻干燥的物料通常比干草的蛋白质降解少，但无芒雀麦在24小时时干草的蛋白质降解率低于冷冻干燥样本。饲草的蛋白质降解差异很大，取决于植物成熟度和保存方法。
