J Anim Sci. 2017 Dec;95(12):5617-5628. doi: 10.2527/jas2017.1974.
The addition of dietary fiber can alter nutrient and N utilization in precision-fed dairy heifers and may further benefit from higher inclusion levels of RUP. The objective of this experiment was to determine the effects of feeding a high-RUP diet when dietary fiber content was manipulated within differing forage-to-concentrate ratios (F:C) on nutrient utilization of precision-fed dairy heifers. Six rumen-cannulated Holstein heifers (555.4 ± 31.4 kg BW; 17.4 ± 0.1 mo) were randomly assigned to 2 levels of forage, high forage (HF; 60% forage) or low forage (LF; 45% forage), and to a fiber proportion sequence (low fiber: 100% oat hay and silage [OA], 0% wheat straw [WS]; medium fiber: 83.4% OA, 16.6% WS; and high fiber: 66.7% OA, 33.3% WS) administered according to a split-plot 3 × 3 Latin square design (21-d periods). Similar levels of N intake (1.70 g N/kg BW) and RUP (55% of CP) were provided. Data were analyzed as a split-plot, 3 × 3 Latin square design using a mixed model with fixed effects of period and treatment. A repeated measures model was used with data that had multiple measurements over time. No differences were observed for DM, OM, NDF, or ADF apparent digestibility coefficients (dC) between HF- and LF-fed heifers. Heifers receiving LF diets had greater starch dC compared to HF heifers. Increasing the fiber level through WS addition resulted in a linear reduction of OM dC. There was a linear interaction for DM dC with a concurrent linear interaction in NDF dC. Nitrogen intake, dC, and retention did not differ; however, urine and total N excretion increased linearly with added fiber. Predicted microbial CP flow (MP) linearly decreased with WS inclusion mainly in LF heifers, as indicated by a significant interaction between F:C and WS. Rumen pH linearly increased with WS addition, although no F:C effect was detected. Ruminal ammonia concentration had an opposite linear effect with respect to MP as WS increased. Diets with the higher proportion of fiber benefited the most from a high RUP supply, complementing the substantial reduction in predicted MP caused by the incremental dietary fiber concentration. These results suggest that RUP supplementation is a practical method for reestablishing optimal ruminal N balance in the event of increased dietary fiber through forage inclusion in precision-fed dairy heifer diets.
日粮纤维的添加可以改变精准饲养奶牛的养分和氮利用，并且可能会从更高水平的瘤胃非蛋白氮（RUP）添加中获益更多。本试验的目的是确定在不同饲草与精料比（F:C）下，当饲料中 RUP 水平较高时，通过调整日粮纤维含量，对精准饲养奶牛的养分利用的影响。6 头瘤胃切开的荷斯坦奶牛（555.4±31.4kg BW；17.4±0.1 月龄）随机分为 2 个饲草水平，高饲草（HF；60%饲草）或低饲草（LF；45%饲草），并按照分割区组 3×3 拉丁方设计（21d 期）分配到纤维比例序列（低纤维：100%燕麦干草和青贮料[OA]，0%小麦秸秆[WS]；中纤维：83.4%OA，16.6%WS；高纤维：66.7%OA，33.3%WS）。提供相似水平的氮摄入（1.70g N/kg BW）和 RUP（CP 的 55%）。数据采用固定效应周期和处理的分割区组 3×3 拉丁方设计进行分析。采用具有时间上多次测量的重复测量模型对数据进行分析。HF 和 LF 饲养的奶牛之间，干物质（DM）、有机物（OM）、中性洗涤纤维（NDF）或酸性洗涤纤维（ADF）表观消化系数（dC）没有差异。接受 LF 日粮的奶牛的淀粉 dC 高于 HF 奶牛。通过添加 WS 增加纤维水平会导致 OM dC 呈线性下降。DM dC 存在线性互作，同时 NDF dC 也存在线性互作。氮摄入、dC 和保留没有差异；然而，尿液和总氮排泄量随着纤维的添加呈线性增加。预测微生物 CP 流量（MP）随着 WS 的添加呈线性下降，主要是在 LF 奶牛中，这表明 F:C 和 WS 之间存在显著的互作。瘤胃 pH 随着 WS 的添加呈线性增加，尽管没有检测到 F:C 效应。瘤胃氨浓度与 MP 呈相反的线性效应，随着 WS 的增加而降低。高纤维比例的日粮最受益于高水平的 RUP 供应，补充了由于日粮纤维浓度增加而导致的预测 MP 大量减少。这些结果表明，在精准饲养奶牛日粮中通过增加饲草来增加日粮纤维时，RUP 补充是重新建立最佳瘤胃氮平衡的一种实用方法。
