College of Pastoral Science and Technology, University of Lanzhou, Lanzhou, China.
Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada (AAFC), Lethbridge, AB, Canada.
J Anim Sci. 2021 Jan 1;99(1). doi: 10.1093/jas/skab011.
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.
本研究旨在探讨大麦加工指数（PI）和饲粮未消化中性洗涤纤维（uNDF）浓度对育肥牛干物质（DM）采食量、咀嚼活动、瘤胃 pH 和发酵特性、全消化道消化率、胃肠道屏障功能和血液代谢物的影响。PI 以加工后的密度与加工前密度的百分比表示，PI 越小表示加工越充分。采用 6 头安装瘤胃瘘管的育肥牛（平均体重 715 ± 29kg），采用 6×6 拉丁方设计，设 3 个 PI（65%、75%和 85%）×2 个 uNDF 浓度（低和高；分别占 DM 的 4.6%和 5.6%）处理。育肥牛自由采食由 10%大麦青贮（低 uNDF）、5%青贮和 5%秸秆（高 uNDF）、87%干压大麦和 3%矿物质及维生素补充料组成的全混合日粮。PI×uNDF 存在互作（P＜0.01），表现在 DM 采食量、反刍和总咀嚼时间以及全消化道 DM 消化率方面。低和高 uNDF 饲粮间 DM、有机物（OM）、淀粉和粗蛋白（CP）采食量无差异（P＞0.14），但高 uNDF 饲粮的 NDF 和酸性洗涤纤维采食量更高（P=0.01），而与大麦 PI 无关。高 uNDF 饲粮组育肥牛的采食时间（min/d 或 min/kg DM）更长（P=0.05），总咀嚼时间（min/kg DM）也有增加的趋势（P=0.10），高于低 uNDF 饲粮组。此外，高 uNDF 饲粮育肥牛对长颗粒（＞19mm）进行了挑食（P=0.01），而低 uNDF 饲粮组没有这种情况。改变大麦 PI 对总挥发性脂肪酸（VFA）浓度、各 VFA 摩尔百分比或瘤胃 pH＜5.8 和＜5.6 的持续时间没有影响（P＞0.12）。高 uNDF 饲粮的总 VFA 浓度更低（P=0.01），乙酸比例更大（P=0.01），瘤胃 pH＜5.8 和＜5.6 的持续时间更短（P=0.05）。与高 uNDF 饲粮相比，PI 为 65%和 75%的低 uNDF 饲粮的 DM、OM 和 CP 消化率更高（P=0.02），而 PI 为 85%时，低和高 uNDF 饲粮间无差异。血液代谢物和胃肠道屏障功能不受处理影响（P≥0.10）。这些结果表明，增加饲粮 uNDF 浓度是改善育肥牛瘤胃 pH 状态的有效策略，而不论谷物加工程度如何，而操纵大麦加工程度并不能降低瘤胃酸中毒的风险。
