Khafipour E, Krause D O, Plaizier J C
Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
J Dairy Sci. 2009 Apr;92(4):1712-24. doi: 10.3168/jds.2008-1656.
A study was conducted to determine if subacute ruminal acidosis (SARA) induced by feeding alfalfa pellets results in increases in free bacterial lipopolysaccharide (LPS) in rumen fluid and peripheral blood, and acute phase proteins in plasma, and to determine the effect of alfalfa pellet-induced SARA on feed intake, rumen fermentation characteristics, milk production and composition, and blood metabolites. Eight lactating Holstein cows, 4 of which were ruminally cannulated, were used in a 6-wk experiment and were fed once daily at 0900 h. During wk 1, cows received a diet containing 50% of DM as concentrate and 50% of DM chopped alfalfa hay. Between wk 2 and wk 6, alfalfa hay was gradually replaced with alfalfa pellets at the rate of 8% per week to reduce rumen pH. Rumen pH was monitored continuously in the ruminally cannulated cows using indwelling pH probes. Rumen fluid and peripheral blood were sampled 15 min before feed delivery and at 6 h after feed delivery. Based on adopted threshold of SARA of at least 180 min/d below pH 5.6, SARA was induced from wk 3 onwards. Replacing 40% of alfalfa hay with alfalfa pellets quadratically increased the DMI from 18.1 kg/d in wk 1 to 23.4 kg/d in wk 6. This replacement linearly decreased milk yield (32.7 vs. 35.9 kg/d) and milk fat percentage and yield (2.32 vs. 3.22%, and 0.77 vs. 1.14 kg/d, respectively), but increased milk protein percentage and yield (3.80 vs. 3.04%, and 1.23 vs. 1.07 kg/d, respectively). This gradual replacement also linearly increased the daily averages of total volatile fatty acids (90 to 121.9 mM), acetate (53.9 to 66.8 mM), propionate (21.5 to 39.6 mM), and osmolality (277.7 to 293.8 mmol/kg) in the rumen and decreased the acetate to propionate ratio from 2.62 to 1.73. Replacing alfalfa hay with alfalfa pellets linearly increased blood lactate from 1.00 mM in wk 1 to a peak of 3.46 mM in wk 5. Induction of SARA in this study increased free rumen LPS concentration from 42,122 endotoxin unit (EU)/mL in wk 1 to 145,593 EU/mL in wk 6. However, this increase was not accompanied by an increase in LPS (<0.05 EU/mL) and in acute phase proteins serum amyloid-A, haptoglobin, and LPS-binding protein in peripheral circulation. Results suggest that SARA induced by alfalfa pellets increased LPS in the rumen without causing translocation of LPS and an immune response.
本研究旨在确定饲喂苜蓿颗粒诱导的亚急性瘤胃酸中毒（SARA）是否会导致瘤胃液和外周血中游离细菌脂多糖（LPS）增加、血浆中急性期蛋白增加，并确定苜蓿颗粒诱导的SARA对采食量、瘤胃发酵特性、产奶量和乳成分以及血液代谢物的影响。选用8头泌乳期荷斯坦奶牛，其中4头安装了瘤胃瘘管，进行为期6周的试验，每天09:00饲喂一次。在第1周，奶牛采食的日粮中精料占干物质的50%，切碎的苜蓿干草占干物质的50%。在第2周至第6周期间，苜蓿干草以每周8%的速度逐渐被苜蓿颗粒取代，以降低瘤胃pH值。使用植入式pH探头对安装瘤胃瘘管的奶牛的瘤胃pH值进行连续监测。在饲喂前15分钟和饲喂后6小时采集瘤胃液和外周血。根据采用的SARA阈值，即pH值低于5.6的时间至少为180分钟/天，从第3周开始诱导出SARA。用苜蓿颗粒替代40%的苜蓿干草，使干物质采食量从第1周的18.1千克/天呈二次曲线增加到第6周的23.4千克/天。这种替代使产奶量（分别为32.7千克/天和35.9千克/天）、乳脂率和乳脂产量（分别为2.32%和3.22%，以及0.77千克/天和1.14千克/天）呈线性下降，但使乳蛋白率和乳蛋白产量（分别为3.80%和3.04%，以及1.23千克/天和1.07千克/天）增加。这种逐渐替代还使瘤胃中总挥发性脂肪酸（从90毫摩尔/升增加到121.9毫摩尔/升）、乙酸（从53.9毫摩尔/升增加到66.8毫摩尔/升）、丙酸（从21.5毫摩尔/升增加到39.6毫摩尔/升）和渗透压（从277.7毫摩尔/千克增加到293.8毫摩尔/千克）的日平均值呈线性增加，并使乙酸与丙酸的比例从2.62降至1.73。用苜蓿颗粒替代苜蓿干草使血液乳酸从第1周的1.00毫摩尔/升线性增加到第5周的峰值3.46毫摩尔/升。本研究中诱导的SARA使瘤胃中游离LPS浓度从第1周的42,122内毒素单位（EU）/毫升增加到第6周的145,593 EU/毫升。然而，这种增加并未伴随着外周循环中LPS（<0.05 EU/毫升）以及急性期蛋白血清淀粉样蛋白A、触珠蛋白和LPS结合蛋白的增加。结果表明，苜蓿颗粒诱导的SARA会增加瘤胃中的LPS，但不会导致LPS移位和免疫反应。
