Elizalde J C, Merchen N R, Faulkner D B
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
J Dairy Sci. 1999 Sep;82(9):1978-90. doi: 10.3168/jds.S0022-0302(99)75434-2.
We compared ruminal dry matter (DM) and crude protein (CP) degradation kinetics of fresh forages of alfalfa (vegetative, early bud, early flowering, and late flowering stages) and bromegrass with endophyte-free and endophyte-infected tall fescue (tillering, stem elongation, heading, and flowering stages) by using nonlinear models. Duplicate Dacron bags were incubated for 0, 3, 6, 9, 12, 16, 24, 36, 48, and 60 h in 2 Simmental x Angus steers fitted with ruminal cannulas. The effects of animal, forage species, and maturity within forage species were evaluated. A first-order kinetics model was determined to be suitable for estimation of degradation profiles relative to models with variable rate of degradations. Alfalfa had higher soluble DM (36.6%), lower insoluble potentially digestible DM (43.0%), higher rate (13.8%/h), and higher extent of DM degradation (66.3%) than grasses (27.2, 53.5, 6.7%/h, and 54.6% for soluble DM, insoluble potentially digestible DM, rate, and extent of DM degradation, respectively). The extent of CP degradation was similar among forages (74.7%), but alfalfa had a higher CP degradation rate than grasses (16.1 vs. 12.5%/h). Extents of degradation of DM and CP decreased with maturity in alfalfa and in grasses. Ruminally undegradable CP (RUP) was higher in alfalfa (40.0 g/kg of DM) than in grasses (34.9 g/kg of DM), and decreased with maturity in grasses (40.4 to 28.3 g/kg of DM) but not in alfalfa. The amount of RUP that was potentially degradable in the rumen was not different among forage species (22.1 g/kg). As forage CP concentration decreased, the RUP (as a percentage of CP) increased but, as a percentage of forage DM, decreased. Species of forage had important effects on ruminal DM and CP degradation when incubated in fresh form.
我们使用非线性模型比较了苜蓿（营养期、初花期、盛花期和终花期）和无芒雀麦等新鲜牧草，以及内生真菌未感染和感染的高羊茅（分蘖期、拔节期、抽穗期和开花期）的瘤胃干物质（DM）和粗蛋白（CP）降解动力学。将装有重复涤纶袋的样品在2头装有瘤胃瘘管的西门塔尔×安格斯阉牛体内分别培养0、3、6、9、12、16、24、36、48和60小时。评估了动物、牧草种类以及牧草种类内成熟度的影响。相对于具有可变降解速率的模型，确定一阶动力学模型适合估计降解曲线。苜蓿的可溶性干物质含量较高（36.6%），不可溶性潜在可消化干物质含量较低（43.0%），降解速率较高（13.8%/小时），干物质降解程度较高（66.3%），而禾本科牧草的相应数值分别为27.2%、53.5%、6.7%/小时和54.6%。各牧草的粗蛋白降解程度相似（74.7%），但苜蓿的粗蛋白降解速率高于禾本科牧草（16.1%/小时对12.5%/小时）。苜蓿和禾本科牧草中，干物质和粗蛋白的降解程度均随成熟度增加而降低。苜蓿中瘤胃不可降解粗蛋白（RUP）含量高于禾本科牧草（40.0克/千克干物质对34.9克/千克干物质），禾本科牧草中RUP含量随成熟度增加而降低（40.4至28.3克/千克干物质），而苜蓿中则无此变化。瘤胃中潜在可降解的RUP量在各牧草种类间无差异（22.1克/千克）。随着牧草粗蛋白浓度降低，RUP（占粗蛋白的百分比）增加，但占牧草干物质的百分比降低。新鲜状态下培养时，牧草种类对瘤胃干物质和粗蛋白降解有重要影响。
