Bach A, Yoon I K, Stern M D, Jung H G, Chester-Jones H
Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
J Dairy Sci. 1999 Jan;82(1):153-60. doi: 10.3168/jds.S0022-0302(99)75219-7.
Eight single-flow continuous culture fermenters were used to study the effects of the type of energy source on ruminal N utilization from high quality pasture. The four dietary treatments included high quality grass and legume pasture alone (50:50; wt/wt), pasture plus soybean hulls, pasture plus beet pulp, and pasture plus corn. Diets supplemented with additional sources of energy (soybean hulls, beet pulp, and corn) were isocaloric but differed in the type and rate of carbohydrate fermentation. Energy supplements constituted 45% of the total dietary dry matter and were fed twice daily at 12-h intervals in place of pasture, which is characteristic of grain feeding at milking when animals are in a grazing situation. Energy supplementation reduced pH, NH3 N flow, and NH3 N concentration and increased bacterial N flow (as a percentage of N intake). The supplementation of corn and soybean hulls resulted in the highest microbial N flow (as a percentage of N intake). Corn had a tendency to reduce fiber digestion because of excessively low NH3 N concentrations. Beet pulp was similar to corn in that it decreased NH3 N concentrations. Supplementation of soybean hulls resulted in a more synchronized fermentation, greater volatile fatty acid production, and greater fiber digestion. Nitrogen utilization by microbes was maximized by supplementation with soybean hulls or corn twice a day. With diets based on pasture, it may be more important to improve bacterial N flow and bacterial utilization of N than to maximize the efficiency of bacterial protein synthesis because better utilization of N by ruminal microorganisms results in higher bacterial N flow and higher fiber digestion.
使用八个单流连续培养发酵罐研究能量源类型对优质牧草瘤胃氮利用的影响。四种日粮处理包括单独的优质禾本科和豆科牧草（50:50；重量/重量）、牧草加大豆皮、牧草加甜菜粕和牧草加玉米。补充额外能量源（大豆皮、甜菜粕和玉米）的日粮等热量，但碳水化合物发酵的类型和速率不同。能量补充料占日粮总干物质的45%，每天分两次以12小时间隔投喂，以替代牧草，这是动物处于放牧状态下挤奶时谷物饲喂的特点。能量补充降低了pH值、氨氮流量和氨氮浓度，并增加了细菌氮流量（占氮摄入量的百分比）。补充玉米和大豆皮导致最高的微生物氮流量（占氮摄入量的百分比）。由于氨氮浓度过低，玉米有降低纤维消化的趋势。甜菜粕与玉米相似，它降低了氨氮浓度。补充大豆皮导致发酵更同步、挥发性脂肪酸产量更高和纤维消化更好。通过每天两次补充大豆皮或玉米，微生物对氮的利用最大化。对于以牧草为基础的日粮，提高细菌氮流量和细菌对氮的利用可能比最大化细菌蛋白质合成效率更重要，因为瘤胃微生物对氮的更好利用会导致更高的细菌氮流量和更高的纤维消化。
