Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
J Anim Sci. 2013 Jun;91(6):2812-22. doi: 10.2527/jas.2012-5982. Epub 2013 Mar 11.
Four experiments were conducted to evaluate RUP content and digestibility for smooth bromegrass, subirrigated meadow, upland native range, and warm-season grasses. Samples were collected from esophageally cannulated cows or ruminally cannulated steers. Forages were ruminally incubated in in situ bags for durations of time based on 75% of total mean retention time, which was based on IVDMD and rate of passage calculations. One-half of the bags were duodenally incubated and excreted in the feces, and NDIN was analyzed on all bags for RUP calculations. Crude protein was numerically greater early in the growing cycle for grasses compared with later as grasses matured (P ≤ 0.32). The RUP was 13.3%, 13.3%, and 19.7% of CP for smooth bromegrass, subirrigated meadow, and upland native range, respectively. These values tended to be lower early in the growth cycle and increased (linear P ≤ 0.13) as forages matured for warm-season grasses and subirrigated meadows. Because both CP and RUP content change throughout the growing season, expressing RUP as a percentage of DM gives more consistent averages compared with RUP as a percentage of CP. Coefficient of variation values for RUP as a percentage of DM averaged 0.21 over all 4 experiments compared with 0.26 for RUP as a percentage of CP. Average RUP as a percentage of DM was 2.03%, 1.53%, and 1.94% for smooth bromegrass, subirrigated meadow, and upland native range, respectively. Total tract indigestible protein (TTIDP) linearly increased with maturity for subirrigated meadow samples (P < 0.01). A quadratic response (P ≤ 0.06) for TTIDP was observed in smooth bromegrass and warm-season grass samples. Digestibility of RUP varied considerably, ranging from 25% to 60%. Subirrigated meadow, native range, and smooth bromegrass samples tended to have linear decreases (P ≤ 0.11) in RUP digestibility throughout the growing season. The amount of digested RUP was fairly consistent across experiments and averages for smooth bromegrass, subirrigated meadow, and upland native range were 0.92%, 0.64%, and 0.49% of DM, respectively. Warm-season grasses in Exp. 2 had greater RUP (4.31% of DM) and amount of RUP digested (2.26% of DM), possibly because of cattle selecting for leadplant that contains more CP than the grasses. Forages can vary in CP, RUP, TTIDP, and RUP digestibility depending on the forage type, year, and time within year, but RUP digestibility is likely less than what previous sources have reported.
进行了四项实验来评估光滑臂形草、地下水位补灌草地、旱地原生草原和暖季草地的 RUP 含量和消化率。样品取自食管插管奶牛或瘤胃插管阉牛。牧草在体内消化袋中进行瘤胃孵育,孵育时间基于 IVDMD 和通过时间计算的 75%总平均滞留时间。一半的袋子进行十二指肠孵育,并在粪便中排出,所有袋子的 NDIN 用于 RUP 计算。与牧草成熟时相比,在生长周期早期,牧草的粗蛋白数值更高(P≤0.32)。光滑臂形草、地下水位补灌草地和旱地原生草原的 RUP 分别为 CP 的 13.3%、13.3%和 19.7%。对于暖季草地和地下水位补灌草地,这些值在生长周期早期较低,并随着牧草成熟而增加(线性 P≤0.13)。由于整个生长季节 CP 和 RUP 含量都在变化,因此将 RUP 表示为 DM 的百分比比将 RUP 表示为 CP 的百分比能提供更一致的平均值。与 RUP 作为 CP 的百分比相比,4 项实验中 RUP 作为 DM 的百分比的变异系数值平均为 0.21,而 RUP 作为 CP 的百分比的变异系数值平均为 0.26。光滑臂形草、地下水位补灌草地和旱地原生草原的 RUP 作为 DM 的百分比平均值分别为 2.03%、1.53%和 1.94%。地下水位补灌草地样品的总可消化蛋白(TTIDP)随成熟度呈线性增加(P<0.01)。在地下水位补灌草地和暖季草地样品中观察到 TTIDP 的二次响应(P≤0.06)。RUP 消化率变化很大,范围为 25%至 60%。在整个生长季节,地下水位补灌草地、原生草原和光滑臂形草样品的 RUP 消化率呈线性下降(P≤0.11)。跨实验的消化 RUP 量相当一致,光滑臂形草、地下水位补灌草地和旱地原生草原的平均值分别为 DM 的 0.92%、0.64%和 0.49%。实验 2 中的暖季草地的 RUP(DM 的 4.31%)和消化 RUP 的量(DM 的 2.26%)较大,这可能是因为牛选择了含 CP 量高于牧草的铅草。牧草的 CP、RUP、TTIDP 和 RUP 消化率会因牧草类型、年份和年内时间而异,但 RUP 消化率可能低于之前的来源报告。