Accurate analysis of degradability of silage neutral detergent fiber (NDF) is important for diet formulation and to predict lactational performance of dairy cows. In this study, 5 corn silage hybrids ensiled for 0 (unfermented), 30, 60, 120, and 150 d were used to determine the effects of ensiling time on silage neutral detergent fiber degradability (NDFD) and to assess the relationships between near-infrared reflectance spectroscopy (NIR) NDF-related analyses and in situ NDFD variables. In addition, the relationships between dietary concentration of indigestible NDF, 288-h incubation (iNDF288), or undegraded NDF, 240-h incubation (uNDF240), and in vivo total-tract apparent organic matter and NDF digestibility were studied in total mixed ration samples from 16 experiments with lactating dairy cows. Ensiling time had no effect on silage NDF concentration; however, the ratio of acid detergent fiber ÷ NDF increased, and estimated hemicellulose concentration decreased quadratically with ensiling time. Also, concentration of NDF-bound protein decreased, and that of lignin increased linearly with ensiling time. These changes in silage fiber composition resulted in a linear decrease in in situ effective degradability of silage NDF with increasing ensiling time. The indigestible fraction of NDF and concentration of structural carbohydrates were not affected by ensiling time. Correlations of in situ NDFD variables with laboratory NIR NDFD analyses were weak to moderate. The relationship of corn silage uNDF240 with lignin concentration or 30-h NDFD (all NIR analyses) was remarkably good (R2 = 0.73 and 0.88, respectively). The relationship between in situ iNDF288 concentration (but not uNDF240) and in vivo total-tract apparent digestibility of dietary organic matter and NDF was good (R2 = 0.72 and 0.80, respectively). In conclusion, in situ degradability of silage NDF linearly decreased from 0 to 150 d ensiling time, primarily caused by a decrease in concentrations of hemicellulose and NDF-bound protein. In situ NDF degradability measurements and common laboratory NIR NDF-related analyses were generally poorly correlated. We found a good relationship between in vivo NDF digestibility and dietary concentration of iNDF288 determined in situ, but the relationship with uNDF240 was poor.

中文翻译：

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青贮时间对玉米青贮中性洗涤剂纤维降解性的影响以及实验室纤维分析与体内消化率之间的关系。

准确地分析青贮中性洗涤剂纤维（NDF）的降解性对日粮配方和预测奶牛的泌乳性能非常重要。在这项研究中，使用5个青贮的青贮杂种，分别青贮0（未发酵），30、60、120和150 d，以确定青贮时间对青贮中性洗涤剂纤维降解性（NDFD）的影响，并评估近端青贮纤维之间的关系。红外反射光谱（NIR）与NDF相关的分析和原位NDFD变量。此外，在总混合日粮中研究了日粮难消化的NDF，288h孵育（iNDF288）或未降解的NDF，240h孵育（uNDF240）的饮食浓度与体内总道表观有机质和NDF消化率之间的关系。泌乳奶牛的16个实验的样本。包浆时间对青贮饲料中NDF的浓度没有影响。然而，酸性洗涤剂纤维÷NDF的比例增加，估计的半纤维素浓度随包封时间成二次方降低。而且，NDF结合蛋白的浓度降低，而木质素的浓度则随着成藏时间的增加而线性增加。青贮纤维组成的这些变化导致青贮饲料NDF的原位有效降解能力随包裹时间的延长而线性降低。消化时间不影响NDF的难消化部分和结构性碳水化合物的浓度。原位NDFD变量与实验室NIR NDFD分析的相关性是弱到中等的。玉米青贮uNDF240与木质素浓度或30小时NDFD（所有NIR分析）之间的关系非常好（分别为R2 = 0.73和0.88）。iNDF288的原位浓度（而非uNDF240）与体内膳食有机物和NDF的总表观消化率之间的关系很好（R2分别为0.72和0.80）。总之，青贮饲料NDF的原位降解能力从0下降到150 d集中时间，这主要是由于半纤维素和NDF结合蛋白的浓度降低所致。原位NDF可降解性测量结果和实验室NIR相关的NIR相关分析通常相互关联程度较差。我们发现体内NDF消化率与就地测定iNDF288的饮食浓度之间存在良好的关系，但与uNDF240的关系较差。青贮饲料NDF的原位降解能力从0到150 d线性缩短，主要是由于半纤维素和NDF结合蛋白的浓度降低。原位NDF可降解性测量结果和实验室NIR相关的NIR相关分析通常相互关联程度较差。我们发现体内NDF消化率与就地测定iNDF288的饮食浓度之间存在良好的关系，但与uNDF240的关系较差。青贮饲料NDF的原位降解能力从0到150 d线性缩短，主要是由于半纤维素和NDF结合蛋白的浓度降低。原位NDF可降解性测量结果和实验室NIR相关的NIR相关分析通常较差。我们发现体内NDF消化率与就地测定iNDF288的饮食浓度之间存在良好的关系，但与uNDF240的关系较差。