Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, AB Canada.
Department of Animal Poultry Science, University of Saskatchewan, Saskatoon, SK Canada.
J Anim Sci. 2020 Jun 1;98(6). doi: 10.1093/jas/skaa160.
Cattle need physically effective fiber to promote rumination and maintain rumen health, but economics favor the use of low-roughage feedlot diets. The study investigated the optimum barley silage proportion in barley-based finishing diets. Apparent total-tract digestibility (4-d total fecal collection), chewing behavior (6-d video recording), ruminal pH (6-d indwelling pH recording), and fermentation (1 day, sampling 0, 3, 6, 12, and 18 h postfeeding), short-chain fatty acid (SCFA) absorption (washed reticulo-rumen technique), gastrointestinal tract barrier function (marker infusion), and blood variables (catheters) were measured. Eight ruminally fistulated crossbred beef heifers (653 ± 44.2 kg; mean starting body weight [BW] ± SD) were used in a replicated 4 × 4 Latin square design with 28-d periods. Dietary treatments were 0%, 4%, 8%, and 12% of dietary dry matter (DM) as barley silage, with diets containing 80%, 76%, 72%, and 68% barley grain, respectively. Increasing silage proportion decreased dietary starch content from 49.0% to 43.1% DM, while neutral detergent content increased from 22.7% to 25.1% DM. Silage proportion had no effect on DM intake, but apparent DM digestibility decreased quadratically (86.0%, 82.1%, 81.1%, 79.5% for the four diets, respectively; P < 0.001). Although, silage proportion had no effect on eating activity, rumination time increased quadratically (246, 289, 302, 316 min/d; P = 0.04). Increased silage proportion increased minimum (5.07, 5.27, 5.29, 5.41; quadratic, P = 0.011) and mean (5.61, 5.87, 5.93, 5.95; quadratic, P = 0.007) ruminal pH, and there was a quadratic (P ≤ 0.047) decrease in duration and area under the pH acidosis threshold curves of 5.8, 5.5, and 5.2. Although increasing silage proportion decreased ruminal acidosis, it was not completely eliminated even with a diet containing 12% silage DM. SCFA concentration in ruminal fluid was not affected by diet, but silage proportion quadratically (P ≤ 0.088) increased ruminal acetate:propionate. There was no effect of diet on absolute or fractional rates of absorption of acetate, propionate, butyrate or total SCFA, and no effect on gastrointestinal barrier function or blood measurements. In conclusion, responses to roughage level were mostly quadratic with greatest improvements in acidosis variables between 0% and 4% barley silage, with incremental improvements with further increases in silage levels. The study showed a trade-off between maximizing digestibility and energy intake to promote animal performance and minimizing the risk of acidosis.
牛需要物理有效纤维来促进反刍和维持瘤胃健康，但经济因素有利于使用低纤维的饲料场日粮。本研究旨在探讨大麦青贮在基于大麦的育肥日粮中的最佳比例。研究测定了全肠道表观消化率（4 天总粪便收集）、咀嚼行为（6 天视频记录）、瘤胃 pH（6 天留置 pH 记录）、发酵（1 天，采样 0、3、6、12 和 18 小时后）、短链脂肪酸（SCFA）吸收（洗提网胃技术）、胃肠道屏障功能（标记物输注）和血液变量（导管）。使用 8 头瘤胃瘘管杂交肉牛（653±44.2kg；平均起始体重[BW]±SD）进行复制的 4×4 拉丁方设计，每个周期 28 天。日粮处理分别为 0%、4%、8%和 12%的日粮干物质（DM）作为大麦青贮，相应的日粮分别含有 80%、76%、72%和 68%的大麦籽粒。青贮比例的增加使日粮淀粉含量从 49.0%降至 43.1%DM，而中性洗涤剂含量从 22.7%增加到 25.1%DM。青贮比例对干物质摄入量没有影响，但表观干物质消化率呈二次方关系降低（四种日粮分别为 86.0%、82.1%、81.1%和 79.5%；P<0.001）。虽然青贮比例对采食活动没有影响，但反刍时间呈二次方关系增加（246、289、302、316min/d；P=0.04）。增加青贮比例会增加最小（5.07、5.27、5.29、5.41；二次方，P=0.011）和平均（5.61、5.87、5.93、5.95；二次方，P=0.007）瘤胃 pH，5.8、5.5 和 5.2 的 pH 酸中毒阈值曲线的持续时间和面积呈二次方关系下降（P≤0.047）。虽然增加青贮比例可降低瘤胃酸中毒，但即使日粮中含有 12%的青贮 DM，也不能完全消除。瘤胃液中 SCFA 浓度不受日粮影响，但青贮比例呈二次方关系（P≤0.088）增加了瘤胃乙酸：丙酸。日粮对乙酸、丙酸、丁酸或总 SCFA 的绝对或分数吸收速率以及胃肠道屏障功能或血液测量没有影响。总之，对粗饲料水平的反应主要是二次方关系，在 0%和 4%大麦青贮之间，酸中毒变量的改善最大，随着青贮水平的进一步提高，改善程度逐渐增加。该研究表明，在最大限度地提高消化率和能量摄入以促进动物生产性能和最小化酸中毒风险之间存在权衡。
