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.

有机牛饲养鼓励使用饲草丰富的日粮，减少颗粒大小已被建议作为提高饲草利用率和增加奶牛营养摄入量的一种方法。然而，减少饲料颗粒的大小会增加通过率，以及可能的可发酵营养物从瘤胃中流出，并且尚未评估后肠发酵的后果。这项研究评估了减少饲料中的饲料颗粒大小对粪便短链脂肪酸（SCFA）谱和饲喂基于饲喂日粮的奶牛细菌群落结构的影响。将21头有机喂养的泌乳荷斯坦奶牛（4头初产和17头多头；平均偏差和标准偏差703±65 kg体重，135±104天，在牛奶中）分为2组，并按2种日粮中的1种喂养34天。日粮中含有20％的精矿和80％的草料（以干物质计），饲喂的草料几何平均粒径为52毫米（CON； 11头奶牛）作为对照，或者以草料粒径减小至30％的日粮喂养。几何平均大小为7毫米（红色； 10头母牛）。在实验结束时收集粪便样品，并将样品立即在-20°C下冷冻。分析样品的SCFA，并使用16S rRNA测序评估粪便细菌群落。数据显示，总SCFA的浓度不受处理的影响，但RED中牛体内主要的生糖前体丙酸酯的比例往往更高（分别为13.3和13.8±0.1％）。主要细菌门，包括 饲喂的饲草的几何平均粒径为52毫米（CON； 11头母牛），或者饲喂的饲料的几何平均粒径为7毫米（RED； 10头）。在实验结束时收集粪便样品，并将样品立即在-20°C下冷冻。分析样品的SCFA，并使用16S rRNA测序评估粪便细菌群落。数据显示，总SCFA的浓度不受处理的影响，但RED中牛体内主要的生糖前体丙酸酯的比例往往更高（分别为13.3和13.8±0.1％）。主要细菌门，包括 饲喂的饲草的几何平均粒径为52毫米（CON； 11头母牛），或者饲喂的饲料的几何平均粒径为7毫米（RED； 10头）。在实验结束时收集粪便样品，并将样品立即在-20°C下冷冻。分析样品的SCFA，并使用16S rRNA测序评估粪便细菌群落。数据显示，总SCFA的浓度不受处理的影响，但RED中牛体内主要的生糖前体丙酸酯的比例往往更高（分别为13.3和13.8±0.1％）。主要细菌门，包括 在实验结束时收集粪便样品，并将样品立即在-20°C下冷冻。分析样品的SCFA，并使用16S rRNA测序评估粪便细菌群落。数据显示，总SCFA的浓度不受处理的影响，但RED中牛体内主要的生糖前体丙酸酯的比例往往更高（分别为13.3和13.8±0.1％）。主要细菌门，包括 在实验结束时收集粪便样品，并将样品立即在-20°C下冷冻。分析样品的SCFA，并使用16S rRNA测序评估粪便细菌群落。数据显示，总SCFA的浓度不受处理的影响，但RED中牛体内主要的生糖前体丙酸酯的比例往往更高（分别为13.3和13.8±0.1％）。主要细菌门，包括硬毛虫（58.0±0.7％），拟杆菌（26.9±0.4％）和疣状微生物菌（4.0±0.4％）不受饲草粒径的影响。家庭毛螺中的相对丰度增加时，RED饮食喂养（12.1和CON和RED，分别13.9±0.5％），和属Acetitomaculum（1.1和1.8±0.2％），Turicibacter（0.7和0.9±0.1％），和鲁米诺杆菌饲喂RED时，相对丰度增加（0.1和0.4±0.1％）。此外，一些粪便细菌类群的相对丰度与主要粪便的SCFA和pH相关。将草料的颗粒大小从几何平均粒度从52毫米降低到7毫米，可保持粪便中总SCFA浓度，并倾向于提高丙酸酯浓度，而无营养不良的风险。因此，结果表明，降低饲草颗粒尺寸代表了一种优化饲草利用率的有效方法，同时可保持饲喂高饲粮的奶牛的后肠发酵和粪便细菌多样性。