Zebeli Q, Ametaj B N
Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada.
J Dairy Sci. 2009 Aug;92(8):3800-9. doi: 10.3168/jds.2009-2178.
The main objective of this study was to evaluate correlative relationships between rumen lipopolysaccharide (LPS) and mediators of acute phase response with milk fat yield and efficiency in dairy cows challenged with graded amounts of barley grain in the diet. An additional aim of the study was to quantify the intercow variation in relation to milk fat production and acute phase response in cows fed graded amounts of grain. Eight primiparous, lactating Holstein cows (60 d in milk) were assigned to 1 of the 4 total mixed rations containing barley grain at 0, 15, 30, and 45% (dry matter basis) in a replicated 4 x 4 Latin square design. Free rumen LPS, plasma acute phase proteins, and milk fat content were quantified in multiple samples collected on d 5 and 7 of the measurement periods shortly before the morning feeding. Results showed markedly greater concentrations of rumen LPS with increasing dietary grain level. The correlative analysis revealed strong negative relationships between rumen LPS and milk fat content and yield. The predictor variable of rumen LPS explained 69% of the variation during the milk fat reduction of the cows. The stronger depression in milk fat percentage was obtained when rumen LPS exceeded a threshold of 5,564 ng/mL, corresponding to a milk fat content of 3.39%. The increase in concentration of rumen LPS was also associated with declines in milk fat yield and 3.5% fat-corrected milk (R(2) = 0.50), as well as milk energy efficiency (R(2) = 0.43). The correlative analysis also indicated that the increase of plasma C-reactive protein (CRP) in response to higher grain feeding was associated with a linear decrease of milk fat content and yield (R(2) = 0.28 to 0.46). Furthermore, the statistical analysis revealed high percentages of intercow variation related to milk fat variables, as well as the responses of rumen LPS and plasma CRP. Taken together, the current results implicate rumen LPS and the host CRP response in the lowering of milk fat content and milk energy efficiency in dairy cows fed high-grain diets. Further research is warranted to understand the mechanism(s) by which rumen LPS and inflammatory responses to LPS lower milk fat synthesis and milk energy efficiency and to develop novel strategies for their prevention.
本研究的主要目的是评估瘤胃脂多糖（LPS）与急性期反应介质之间的相关性，以及在日粮中添加不同剂量大麦谷物的情况下，这些因素与奶牛乳脂产量和效率之间的关系。本研究的另一个目的是量化不同谷物添加量日粮条件下，奶牛在乳脂产量和急性期反应方面的个体间差异。八头初产泌乳的荷斯坦奶牛（产奶60天）被分配到4种全混合日粮中的一种，日粮中大麦谷物含量分别为0%、15%、30%和45%（干物质基础），采用重复4×4拉丁方设计。在测定期的第5天和第7天早晨饲喂前，采集多个样本，对瘤胃游离LPS、血浆急性期蛋白和乳脂含量进行定量分析。结果表明，随着日粮谷物水平的增加，瘤胃LPS浓度显著升高。相关性分析显示，瘤胃LPS与乳脂含量和产量之间存在强烈的负相关关系。瘤胃LPS预测变量解释了奶牛乳脂减少期间69%的变异。当瘤胃LPS超过5564 ng/mL阈值时，乳脂百分比下降更为明显，此时乳脂含量为3.39%。瘤胃LPS浓度的增加还与乳脂产量和3.5%乳脂校正乳产量下降相关（R² = 0.50），以及与乳能效率下降相关（R² = 0.43）。相关性分析还表明，随着谷物饲喂量增加，血浆C反应蛋白（CRP）升高与乳脂含量和产量呈线性下降相关（R² = 0.28至0.46）。此外，统计分析表明，个体间在乳脂变量以及瘤胃LPS和血浆CRP反应方面存在较高比例的差异。综上所述，目前的研究结果表明，瘤胃LPS和宿主CRP反应与高谷物日粮奶牛的乳脂含量和乳能效率降低有关。有必要进一步研究瘤胃LPS及其对LPS的炎症反应降低乳脂合成和乳能效率的机制，并开发新的预防策略。
