Institute of Animal Nutrition and Functional Plant Compounds, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, 1210, Vienna, Austria.
Division of Livestock Sciences, Department of Sustainable Agricultural Systems, BOKU-University of Natural Resources and Life Sciences, 1180 Vienna, Austria.
J Dairy Sci. 2020 Sep;103(9):8020-8033. doi: 10.3168/jds.2019-18036. Epub 2020 Jun 26.
Organic cattle farming encourages the use of forage-rich diets, and the reduction of particle size has been suggested as an approach to improve forage utilization and enhance nutrient intake of cows. However, reducing forage particle size increases passage rate, as well as the flow of potentially fermentable nutrients out of the rumen, and the consequences for hindgut fermentation have not been evaluated yet. This study evaluated the effects of decreasing dietary forage particle size on the fecal short-chain fatty acid (SCFA) profile and the bacterial community structure of dairy cows fed forage-based rations. Twenty-one organically fed lactating Holstein cows (4 primiparous and 17 multiparous; mean and standard deviation 703 ± 65 kg body weight, 135 ± 104 days in milk) were divided into 2 groups and fed 1 of 2 diets for 34 d. Diets contained 20% concentrate and 80% forage (dry matter basis), and were fed either as a control with a forage geometric mean particle size of 52 mm (CON; 11 cows) or as a diet with the forage particle size reduced to a geometric mean size of 7 mm (RED; 10 cows). Fecal samples were collected at the end of the experiment, and samples were immediately frozen at -20°C. Samples were analyzed for SCFA, and the fecal bacterial community was evaluated using 16S rRNA sequencing. Data showed that the concentration of total SCFA was not affected by treatment, but the proportion of propionate, a key glucogenic precursor in cattle, tended to be greater for RED (13.3 and 13.8 ± 0.1%, respectively). The predominant bacterial phyla, including Firmicutes (58.0 ± 0.7%), Bacteroidetes (26.9 ± 0.4%), and Verrucomicrobia (4.0 ± 0.4%), were not affected by forage particle size. Family Lachnospiraceae increased in relative abundance when the RED diet was fed (12.1 and 13.9 ± 0.5% for CON and RED, respectively), and genera Acetitomaculum (1.1 and 1.8 ± 0.2%), Turicibacter (0.7 and 0.9 ± 0.1%), and Ruminobacter (0.1 and 0.4 ± 0.1%) increased in relative abundance when RED was fed. In addition, relative abundance of some fecal bacterial taxa was correlated with major fecal SCFA and pH. Reducing the particle size of forages, from 52 to 7 mm geometric mean particle size, maintained fecal concentration of total SCFA and tended to enhance propionate concentration, without risk of dysbiosis. Thus, results suggest that reduction of forage particle size represents an effective approach to optimizing forage utilization while maintaining hindgut fermentation and fecal bacterial diversity in dairy cows fed forage-rich diets.
有机奶牛养殖鼓励使用富含草料的饮食，并且已经提出减小颗粒大小是提高草料利用率和增强奶牛营养摄入的一种方法。然而，减小草料颗粒大小会增加通过速度，以及潜在可发酵营养素流出瘤胃的速度，而对后肠发酵的后果尚未进行评估。本研究评估了降低日粮草料颗粒大小对基于草料日粮喂养的奶牛粪便短链脂肪酸 (SCFA) 谱和细菌群落结构的影响。21 头有机喂养的泌乳荷斯坦奶牛（4 头初产和 17 头经产；平均值和标准差为 703 ± 65 kg 体重，135 ± 104 天泌乳期）分为 2 组，分别喂食 2 种日粮中的 1 种，持续 34 天。日粮含有 20%浓缩物和 80%草料（干物质基础），并以控制组（CON；11 头牛）的草料几何平均粒径为 52mm 或粒径减小到 7mm 的实验组（RED；10 头牛）的形式进行喂食。在实验结束时收集粪便样本，并立即将样本在-20°C 下冷冻。对样本进行 SCFA 分析，并使用 16S rRNA 测序评估粪便细菌群落。数据显示，处理对总 SCFA 的浓度没有影响，但 RED 组丙酸的比例（分别为 13.3 和 13.8 ± 0.1%）有增加的趋势。主要细菌门，包括厚壁菌门（58.0 ± 0.7%）、拟杆菌门（26.9 ± 0.4%）和疣微菌门（4.0 ± 0.4%）不受草料粒径的影响。当喂食 RED 日粮时，lachnospiraceae 家族的相对丰度增加（CON 和 RED 分别为 12.1 和 13.9 ± 0.5%），而 Acetitomaculum（1.1 和 1.8 ± 0.2%）、Turicibacter（0.7 和 0.9 ± 0.1%）和 Ruminobacter（0.1 和 0.4 ± 0.1%）的相对丰度增加。此外，一些粪便细菌分类群的相对丰度与主要粪便 SCFA 和 pH 值相关。将草料的粒径从 52 减小到 7 毫米的几何平均粒径，维持了粪便总 SCFA 的浓度，并倾向于增加丙酸的浓度，而不会产生菌群失调的风险。因此，结果表明，减小草料粒径是优化草料利用的有效方法，同时维持了富含草料日粮喂养的奶牛的后肠发酵和粪便细菌多样性。
