The objective of this study was to investigate the effects of processing index (PI) of barley grain and dietary undigested neutral detergent fiber (uNDF) concentration on dry matter (DM) intake, chewing activity, ruminal pH and fermentation characteristics, total tract digestibility, gastrointestinal barrier function, and blood metabolites of finishing beef heifers. The PI was measured as the density after processing expressed as a percentage of the density before processing, and a smaller PI equates to a more extensively processed. Six ruminally cannulated heifers (average body weight, 715 ± 29 kg) were used in a 6 × 6 Latin square design with three PI (65%, 75%, and 85%) × 2 uNDF concentration (low and high; 4.6% vs. 5.6% of DM) factorial arrangement. The heifers were fed ad libitum a total mixed ration consisting of 10% barley silage (low uNDF), or 5% silage and 5% straw (high uNDF), 87% dry-rolled barley grain, and 3% mineral and vitamin supplements. Interactions (P < 0.01) of PI × uNDF were observed for DM intake, ruminating and total chewing time, and DM digestibility in the total digestive tract. Intake of DM, organic matter (OM), starch, and crude protein (CP) did not differ (P > 0.14) between low and high uNDF diets, but intakes of NDF and acid detergent fiber were greater (P = 0.01) for high uNDF diets regardless of barley PI. Heifers fed high uNDF diets had longer (P = 0.05) eating times (min/d or min/kg DM) and tended (P = 0.10) to have longer total chewing times (min/kg DM) than those fed low uNDF diets. Additionally, heifers sorted (P = 0.01) against long particles (>19 mm) for high uNDF diets but not for low uNDF diets. Altering PI of barley grain did not affect (P > 0.12) total volatile fatty acid (VFA) concentration, molar percentages of individual VFA, or duration of ruminal pH < 5.8 and <5.6. Total VFA concentration was less (P = 0.01), acetate percentage was greater (P = 0.01), and duration of ruminal pH < 5.8 and <5.6 was less (P = 0.05) for high compared with low uNDF diets. Digestibility of DM, OM, and CP was greater (P = 0.02) for low vs. high uNDF diets with PI of 65% and 75%, with no difference between low and high uNDF diets at PI of 85%. Blood metabolites and gastrointestinal tract barrier function were not affected (P ≥ 0.10) by the treatments. These results suggest that increasing dietary uNDF concentration is an effective strategy to improve ruminal pH status in finishing cattle, regardless of the extent of grain processing, whereas manipulating the extent of barley processing did not reduce the risk of ruminal acidosis.

中文翻译：

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大麦粒加工指数和日粮中未消化的中性洗涤纤维浓度影响饲喂高谷物日粮的小母牛的咀嚼行为、瘤胃 pH 值和全消化道养分消化率

本研究的目的是研究大麦粒加工指数 (PI) 和日粮未消化中性洗涤纤维 (uNDF) 浓度对干物质 (DM) 摄入量、咀嚼活动、瘤胃 pH 值和发酵特性、总肠道消化率、胃肠道屏障功能和育肥小母牛的血液代谢物。PI 被测量为处理后的密度，表示为处理前的密度的百分比，并且较小的 PI 等同于更广泛的处理。六头瘤胃插管小母牛（平均体重，715 ± 29 kg）用于 6 × 6 拉丁方设计，三个 PI（65%、75% 和 85%）×2 uNDF 浓度（低和高；4.6% vs . 5.6% of DM) 阶乘排列。小母牛随意饲喂由 10% 大麦青贮饲料（低 uNDF）组成的总混合日粮，或 5% 青贮饲料和 5% 稻草（高 uNDF）、87% 干轧大麦粒和 3% 矿物质和维生素补充剂。观察到 PI × uNDF 与 DM 摄入量、反刍和总咀嚼时间以及整个消化道中 DM 消化率的交互作用 (P < 0.01)。低和高 uNDF 日粮对 DM、有机物 (OM)、淀粉和粗蛋白 (CP) 的摄入量没有差异 (P > 0.14)，但 NDF 和酸性洗涤纤维的摄入量在高 uNDF 饮食，与大麦 PI 无关。与饲喂低 uNDF 日粮的小母牛相比，饲喂高 uNDF 日粮的小母牛进食时间（min/d 或 min/kg DM）更长（P = 0.05），并且倾向于（P = 0.10）总咀嚼时间（min/kg DM）更长。此外，对于高 uNDF 日粮，但对于低 uNDF 日粮，小母牛针对长颗粒（＞19 mm）分类（P = 0.01）。改变大麦粒的 PI 不影响 (P > 0.12) 总挥发性脂肪酸 (VFA) 浓度、单个 VFA 的摩尔百分比或瘤胃 pH 值 < 的持续时间。5.8 和＜5.6。总 VFA 浓度较低（P = 0.01），醋酸盐百分比较高（P = 0.01），瘤胃 pH 值 <; 与低 uNDF 饮食相比，高 5.8 和 <5.6 的比例较低 (P = 0.05)。低 uNDF 日粮与高 uNDF 日粮的 DM、OM 和 CP 消化率更高（P = 0.02），PI 为 65% 和 75%，低 uNDF 日粮和高 uNDF 日粮在 PI 为 85% 时没有差异。血液代谢物和胃肠道屏障功能未受到治疗的影响（P ≥ 0.10）。这些结果表明，增加日粮 uNDF 浓度是改善育肥牛瘤胃 pH 值的有效策略，