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首页> 美国卫生研究院文献>Cambridge Open Access >Magnesium absorption as influenced by the rumen passage kinetics in lactating dairy cows fed modified levels of fibre and protein
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Magnesium absorption as influenced by the rumen passage kinetics in lactating dairy cows fed modified levels of fibre and protein

机译：饲喂改良水平的纤维和蛋白质的泌乳奶牛瘤胃通过动力学对镁吸收的影响

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The potassium sensitive magnesium absorption through the rumen wall may be influenced by additional dietary properties, such as diet type, forage type or forage to concentrate ratio. These properties are likely associated to rumen passage kinetics modified by dietary fibre content. The study aimed to assess the effects of rumen passage kinetics on apparent Mg absorption and retention in lactating dairy cows fed modified levels of fibre. Six lactating Red-Holstein and Holstein cows, including four fitted with ruminal cannulas were randomly assigned to a 3 × 3 cross-over design. The experimental diets consisted of early harvested low NDF (341 g NDF/kg DM) and late harvested high NDF (572 g NDF/kg DM) grass silage (80% DM) and of concentrates (20% of DM). As the low-fibre diet was excessive in protein, a third high-fibre diet was formulated to be balanced in digestible protein with the low-fibre diet to avoid any eventual confounding effects of NDF and protein excess. All diets were formulated to contain iso-Ca, -P, -Mg, -K and -Na. Passage kinetics of solid and liquid phase of rumen digesta were evaluated using ruminal marker disappearance profiles. Cows fed the low-fibre diet had compared to the other diets, an up to 40% lower solid and 26% lower liquid phase volume of rumen digesta and a 10% numerically higher fractional rumen liquid passage rate. Rumen pH lost 0.6 units and Mg concentration in the rumen liquid phase tripled when cows were fed the low-fibre diet. Faecal Mg excretion was up to 14% higher in cows fed the low-fibre diet and Mg absorbability was 12% compared to up to 19% in other diets. Urinary Mg excretion in cows fed the low-fibre diet was half of the ones in the other treatments, but Mg retention was not affected. Dietary protein excess neither affected rumen passage kinetics nor Mg absorption and retention. Absorption of Mg was correlated with rumen liquid volume which both decreased with decreasing daily NDF intake (NDFi, 11.8 ± 2.4 l/kg NDFi). Consequently, daily Mg absorption decreased by 1.32 ± 0.28 g/kg decreasing NDFi. To conclude, in addition to the known antagonistic effect of dietary K, the present data indicate that Mg absorption was dependent from NDFi which modified rumen liquid volume, but was independent of dietary protein excess likely associated to low NDF herbages.
机译：通过瘤胃壁对钾敏感的镁的吸收可能受到其他饮食特性的影响，例如饮食类型，饲料类型或饲料与精料的比例。这些特性可能与通过膳食纤维含量改变的瘤胃通过动力学有关。该研究旨在评估瘤胃通过动力学对饲喂改良纤维水平的泌乳奶牛表观镁吸收和and留的影响。随机将6头泌乳的Red-Holstein和Holstein母牛（包括4头装有瘤胃插管的母牛）分配为3×3交叉设计。实验饮食包括早期收获的低NDF（341 g NDF / kg DM）和晚期收获的高NDF（572 g NDF / kg DM）草青贮饲料（80％DM）和浓缩物（DM的20％）。由于低纤维饮食中蛋白质含量过高，因此制定了第三种高纤维饮食，以使可消化蛋白质与低纤维饮食之间保持平衡，从而避免了NDF和蛋白质过量的最终混杂效应。所有饮食均配制为含有iso-Ca，-P，-Mg，-K和-Na。使用瘤胃标记消失曲线评估瘤胃消化物固相和液相的通过动力学。与其他饮食相比，饲喂低纤维饮食的牛瘤胃消化物的固体含量降低了40％，液相体积降低了26％，瘤胃液体的分数通过率提高了10％。当饲喂低纤维日粮时，瘤胃的pH值降低了0.6个单位，瘤胃液相中的Mg浓度增加了两倍。用低纤维日粮喂养的奶牛粪便中的镁排泄量高出14％，而其他日粮中的镁吸收率高达19％。饲喂低纤维饮食的母牛尿中镁的排泄量是其他方法的一半，但镁保留不受影响。饮食中的蛋白质过量既不影响瘤胃通过动力学，也不影响镁的吸收和保留。镁的吸收与瘤胃液量相关，瘤胃液量均随着每日NDF摄入量的减少而降低（NDFi，11.8±2.4 l / kg NDFi）。因此，每天的镁吸收量降低了1.32±0.28 g / kg，从而降低了NDFi。总之，除了已知的膳食K拮抗作用外，目前的数据还表明，镁的吸收还依赖于NDFi，而NDFi改变了瘤胃液量，但不依赖于与低NDF牧草有关的膳食蛋白质过量。

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