Department of Animal Science, University of Manitoba, Winnipeg, MB, Canada.
J Dairy Sci. 2012 Jan;95(1):294-303. doi: 10.3168/jds.2011-4447.
The effects of a grain-based subacute ruminal acidosis (SARA) challenge (GBSC) and an alfalfa-pellet SARA challenge (APSC) on fermentation and endotoxins in the rumen and in the cecum, as well as on endotoxins in peripheral blood, were determined. Six nonlactating Holstein cows with cannulas in the rumen and cecum were used in the study. A 3×3 Latin square arrangement of treatments with 4-wk experimental periods was adopted. During the first 3 wk of each experimental period, all cows received a diet containing 70% forages [dry matter (DM) basis]. In wk 4 of each period, cows received 1 of the following 3 diets: the 70% forage diet fed during wk 1 to 3 (control), a diet in which 34% of the dietary DM was replaced with grain pellets made of 50% ground wheat and 50% ground barely (GBSC), or a diet in which 37% of dietary DM was replaced with pellets of ground alfalfa (APSC). Rumen pH was monitored continuously using indwelling pH probes, and rumen fluid, blood, cecal digesta, and fecal grab samples were collected immediately before feed delivery at 0900 h and at 6 h after feed delivery on d 3 and 5 of wk 4. The time for which rumen pH was below 5.6 was 56.4, 225.2, and 298.8 min/d for the control, APSC, and GBSC treatments, respectively. Compared with the control, SARA challenges resulted in similar reductions in cecal digesta pH, which were 7.07, 6.86, and 6.79 for the control, APSC, and GBSC treatments, respectively. Compared with the control, only GBSC increased starch content in cecal digesta, which averaged 2.8, 2.6, and 7.4% of DM for the control, APSC, and GBSC, respectively. Free lipopolysaccharide endotoxin (LPS) concentration in rumen fluid increased from 10,405 endotoxin units (EU)/mL in the control treatment to 30,715 and 168,391 EU/mL in APSC and GBSC, respectively. Additionally, GBSC increased the LPS concentration from 16,508 to 118,522 EU/g in wet cecal digesta, and from 12,832 to 93,154 EU/g in wet feces. The APSC treatment did not affect LPS concentrations in cecal digesta and feces. All concentrations of LPS in blood plasma were below the detection limit of >0.05 EU/mL of the technique used. Despite the absence of LPS in blood, only GBSC increased the concentration of LPS-binding protein in blood plasma, which averaged, 8.9, 9.5, and 12.1mg/L for the control, APSC, and GBSC treatments, respectively. This suggests that GBSC caused translocation of LPS from the digestive tract but that LPS was detoxified before entering the peripheral blood circulation. The higher LPS concentration in cecal digesta in the GBSC compared with the APSC suggests a higher risk of LPS translocation in the large intestine in GBSC than in APSC.
本研究旨在探讨谷物型亚急性瘤胃酸中毒（SARA）挑战（GBSC）和苜蓿-颗粒 SARA 挑战（APSC）对瘤胃和盲肠发酵及内毒素、外周血内毒素的影响。试验选用 6 头安装有瘤胃和盲肠瘘管的非泌乳荷斯坦奶牛，采用 3×3 拉丁方设计，每个试验期为 4 周。在每个试验期的前 3 周，所有奶牛均饲喂含 70%粗饲料（干物质基础）的日粮。在每个试验期的第 4 周，奶牛分别接受以下 3 种日粮之一：1）第 1 至 3 周饲喂的 70%粗饲料日粮（对照组）；2）用 50%小麦和 50%大麦制成的颗粒日粮（34%日粮干物质由颗粒代替，GBSC）；3）用苜蓿颗粒日粮（37%日粮干物质由颗粒代替，APSC）。采用瘤胃内置探头连续监测瘤胃 pH 值，在第 4 周的第 3 天和第 5 天 0900 时和 0600 时（饲喂后 6 小时），在饲喂前采集瘤胃液、血液、盲肠食糜和粪便样本。对照组、APSC 和 GBSC 处理的瘤胃 pH 值低于 5.6 的时间分别为 56.4、225.2 和 298.8min/d。与对照组相比，SARA 挑战导致盲肠食糜 pH 值显著降低，分别为 7.07、6.86 和 6.79。与对照组相比，仅 GBSC 增加了盲肠食糜中淀粉含量，分别为对照组、APSC 和 GBSC 的 2.8%、2.6%和 7.4%。对照组、APSC 和 GBSC 处理的瘤胃液游离脂多糖内毒素（LPS）浓度分别从 10405 内毒素单位（EU）/mL 增加到 30715 和 168391EU/mL。此外，GBSC 还增加了湿盲肠食糜中的 LPS 浓度，从对照组的 16508EU/g 增加到 118522EU/g，从湿粪便中的 12832EU/g 增加到 93154EU/g。APSC 处理对盲肠食糜和粪便中的 LPS 浓度没有影响。血液中 LPS 的所有浓度均低于所用技术检测限>0.05EU/mL。尽管血液中没有 LPS，但只有 GBSC 增加了血液中 LPS 结合蛋白的浓度，分别为对照组、APSC 和 GBSC 的 8.9、9.5 和 12.1mg/L。这表明 GBSC 导致 LPS 从消化道移位，但 LPS 在进入外周血液循环之前被解毒。与 APSC 相比，GBSC 处理的盲肠食糜中 LPS 浓度更高，表明 GBSC 导致大肠中 LPS 易位的风险高于 APSC。
