Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland P61 C996; Department of Animal Science, Cornell University, Ithaca, NY 14853.
Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland P61 C996.
J Dairy Sci. 2020 Dec;103(12):11332-11348. doi: 10.3168/jds.2020-18437. Epub 2020 Oct 15.
The objective of this study was to evaluate the effect of rolled barley grain (RB) supplementation on rumen metabolism, omasal flow of nutrients, and microbial dynamics in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.; PRG)-based diets. Ten ruminally cannulated Holstein cows averaging (mean ± standard deviation) 49 ± 23 d in milk and 513 ± 36 kg of body weight were assigned to 1 of 2 treatments in a switchback design. The treatment diets were PRG only (G) or PRG plus 3.5 kg of dry matter RB (G+RB). The study consisted of three 29-d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. A double marker system was used to quantify nutrient flow entering the omasal canal along with labeled N-ammonium sulfate to measure bacterial, protozoal, and nonmicrobial N flow. Rumen evacuation techniques were used to determine nutrient and microbial pool size, allowing the calculation of fractional rates of digestion and microbial growth. There was no difference in daily milk yield or energy-corrected milk yield between treatments. Milk fat concentration and milk urea N decreased, whereas milk protein concentration increased in cows fed the G+RB diet. During the omasal sampling phase, dry matter intake was higher in cows fed the G+RB diet. Ruminal and total-tract neutral detergent fiber digestibility was lower in G+RB cows; however, no difference was observed in reticulorumen pH. The rumen pool size of fermentable carbohydrate was increased in cows fed the G+RB diet; however, the fractional rate of digestion was decreased. Flow of nonammonia N and bacterial N at the omasal canal increased in cows fed the G+RB diet compared with the G diet. Protozoa N flow was not different between diets; however, protozoa appeared to supply a much larger amount of microbial N and exhibited shorter generation time than previously considered. Feed N ruminal digestibility, corrected for microbial contribution, was similar for both treatments (88.4 and 89.0% for G and G+RB, respectively). In conclusion, RB supplementation did not benefit overall animal performance; however, it reduced ruminal neutral detergent fiber digestibility and increased bacterial N flow. The results demonstrate the large dependence of cows consuming PRG-based diets on microbial N as the main source of nonammonia N supply. Additional quantitative research is required to further describe the supply of nutrients and microbial dynamics in cows consuming PRG-based diets in an effort to determine most limiting nutrients.
本研究旨在评估在饲喂新鲜黑麦草（Lolium perenne L.；PRG）日粮的泌乳奶牛中添加膨化大麦粒（RB）对瘤胃代谢、瘤胃后真胃养分流量和微生物动态的影响。10 头瘤胃可插管的荷斯坦奶牛平均（平均值±标准差）泌乳 49±23d，体重 513±36kg，采用反转设计分配到 2 种处理中的 1 种。处理日粮分别为仅 PRG（G）或 PRG 加 3.5kg 干物质 RB（G+RB）。研究包括 3 个 29d 期，每个时期包括 21d 的日粮适应期和 8d 的数据和样品采集期。使用双标记系统定量进入真胃的养分流量，并用标记的硫酸铵-15N 测量细菌、原虫和非微生物 N 的流量。使用瘤胃排空技术确定养分和微生物库大小，从而计算消化和微生物生长的分数率。两种处理的日奶产量或校正乳脂产量没有差异。饲喂 G+RB 日粮的奶牛乳脂浓度和乳尿素氮降低，而乳蛋白浓度升高。在真胃采样阶段，饲喂 G+RB 日粮的奶牛干物质采食量较高。G+RB 奶牛的瘤胃和全肠道中性洗涤纤维消化率较低；然而，G+RB 奶牛的网胃 pH 没有差异。饲喂 G+RB 日粮的奶牛瘤胃液中可发酵碳水化合物的库大小增加，但消化分数率降低。与 G 日粮相比，饲喂 G+RB 日粮的奶牛真胃后真胃的非氨 N 和细菌 N 流量增加。日粮间原虫 N 流量无差异；然而，原虫似乎提供了比以前认为的更大数量的微生物 N，并且表现出更短的世代时间。考虑到微生物的贡献，饲料 N 在瘤胃中的消化率在两种处理之间相似（G 和 G+RB 分别为 88.4%和 89.0%）。总之，RB 补充剂对整体动物性能没有益处；然而，它降低了瘤胃中性洗涤纤维消化率并增加了细菌 N 流量。结果表明，饲喂 PRG 日粮的奶牛对微生物 N 的依赖性很大，微生物 N 是非氨 N 供应的主要来源。需要进一步的定量研究来进一步描述饲喂 PRG 日粮的奶牛的养分供应和微生物动态，以确定最限制的养分。
