Coblentz W K, Hoffman P C
USDA-ARS, US Dairy Forage Research Center, Marshfield, WI 54449, USA.
J Dairy Sci. 2009 Jun;92(6):2853-74. doi: 10.3168/jds.2008-1920.
Alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hay was made in 96 large-round bales over 3 harvests during 2006 and 2007 to assess the effects of spontaneous heating on dry matter (DM) recovery, in vitro true digestibility (IVTD), and in situ disappearance kinetics of DM. Throughout these harvests, bales were made at preset diameters of 0.9, 1.2, or 1.5 m and at moisture concentrations ranging from 9.3 to 46.6%. Internal bale temperatures were monitored daily during an outdoor storage period, reaching maxima of 77.2 degrees C (MAX) and 1,997 heating degree days >30 degrees C (HDD) for one specific combination of bale moisture, bale diameter, and harvest. Following storage, regressions of DM recovery on HDD and MAX indicated that DM recovery declined linearly in close association with measures of spontaneous heating. For HDD, slopes and intercepts differed across bale diameters, probably because the greater surface area per kilogram of DM for 0.9-m bales facilitated more rapid dissipation of heat than occurred from 1.2- or 1.5-m-diameter bales. Regardless of bale diameter, coefficients of determination were high (r(2) > or = 0.872) when HDD was used as the independent variable. Regressions of DM recovery on MAX also exhibited high r(2) statistics (> or = 0.833) and a common slope across bale diameters (-0.32 percentage units of DM/ degrees C). Changes in concentrations of IVTD during storage (poststorage - prestorage; DeltaIVTD) also were regressed on HDD and MAX. For HDD, the data were best fit with a nonlinear model in which DeltaIVTD became rapidly negative at <1,000 HDD, but was asymptotic thereafter. When MAX was used as the independent variable, a simple linear model (y = -0.23x + 9.5) provided the best fit. In both cases, coefficients of determination were comparable to those for DM recovery (R(2) or r(2) > or =0.820). Changes (poststorage - prestorage) in ruminal DM degradation rate (DeltaK(d)) and effective ruminal degradability of DM (DeltaDEG) were assessed similarly. Although the most appropriate statistical model varied, DeltaK(d) and DeltaDEG both became increasingly negative at low to moderate levels of heating, but generally stabilized thereafter. Both HDD and MAX were excellent predictor variables for both DeltaK(d) and DeltaDEG; r(2) or R(2) statistics ranged from 0.788 to 0.921. Measures of spontaneous heating are consistently effective indicators of DM recovery following storage, as well as good indicators of concurrent changes in IVTD or in situ disappearance of DM for heated alfalfa-orchardgrass hays.
2006年至2007年期间，通过3次收获制作了96个大型圆捆苜蓿（紫花苜蓿）-果园草（鸭茅）干草，以评估自然发热对干物质（DM）回收率、体外真消化率（IVTD）以及DM原位消失动力学的影响。在这些收获过程中，制作的草捆预设直径为0.9、1.2或1.5米，水分含量范围为9.3%至46.6%。在室外储存期间，每天监测草捆内部温度，对于一种特定的草捆湿度、草捆直径和收获组合，温度最高达到77.2摄氏度（MAX）以及1997个大于30摄氏度的热度日（HDD）。储存后，DM回收率对HDD和MAX的回归表明，DM回收率与自然发热指标密切相关且呈线性下降。对于HDD，不同草捆直径的斜率和截距有所不同，可能是因为0.9米草捆每千克DM的表面积更大，比1.2米或1.5米直径的草捆散热更快。无论草捆直径如何，当以HDD作为自变量时，决定系数都很高（r²≥0.872）。DM回收率对MAX的回归也显示出较高的r²统计值（≥0.833）以及不同草捆直径的共同斜率（-0.32%单位的DM/摄氏度）。储存期间IVTD浓度的变化（储存后 - 储存前；ΔIVTD）也对HDD和MAX进行了回归。对于HDD，数据最适合用非线性模型拟合，其中在HDD＜1000时，ΔIVTD迅速变为负值，但此后呈渐近线。当以MAX作为自变量时，一个简单的线性模型（y = -0.23x + 9.5）拟合效果最佳。在这两种情况下，决定系数与DM回收率的相当（R²或r²≥0.820）。瘤胃DM降解率（ΔKd）和DM有效瘤胃降解率（ΔDEG）的变化（储存后 - 储存前）也进行了类似评估。尽管最合适的统计模型各不相同，但在低至中等加热水平下，ΔKd和ΔDEG均变得越来越负，但此后通常趋于稳定。HDD和MAX都是ΔKd和ΔDEG的优秀预测变量；r²或R²统计值范围为0.788至0.921。自然发热指标始终是储存后DM回收率的有效指标，也是加热苜蓿 - 果园草草捆IVTD或DM原位消失同时变化的良好指标。
