Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/3/2009
Publication Date: 11/1/2009
Citation: Coblentz, W.K., Hoffman, P.C. 2009. Effects of Spontaneous Heating in Large Hay Packages on Dry Matter Recovery, In Vitro True Digestibility, and In Situ Kinetics of Ruminal Dry Matter Disappearance [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. Paper No. 299-1. Interpretive Summary:
Technical Abstract: Alfalfa-orchardgrass hays were 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 pre-set bale diameters of 0.9, 1.2, or 1.5 m, and at moisture concentrations ranging from 9.3 to 46.6%. Following storage, regressions of DM recovery on heating degree days > 30oC (HDD) and maximum internal bale temperature (MAX) indicated that DM recovery declined linearly in close association with both measures of spontaneous heating. For HDD, slopes and intercepts differed across bale diameters, but r2 statistics were high (r2 = 0.872) for all bale sizes. Regressions of DM recovery on MAX also exhibited high r2 statistics (= 0.833), and a common slope across bale diameters (-0.32 percentage units of DM/oC). Changes in concentrations of IVTD during storage (poststorage - prestorage; 'IVTD) also were regressed on both HDD and MAX. For HDD, the data were best fit with a nonlinear model in which 'IVTD became rapidly negative at <1000 HDD, but asymptotic thereafter. For MAX, a simple linear model (Y = -0.23x + 9.5) provided the best fit. In each case, r2 or R2 statistics were comparable to those for DM recovery (=0.820). Changes in ruminal DM degradation rate ('Kd) and effective ruminal degradability of DM ('DEG) were assessed similarly. Although the most appropriate statistical model varied, 'Kd and 'DEG 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 'Kd and 'DEG (r2 or R2 = 0.788). Measures of spontaneous heating are effective indicators of DM recovery following storage, as well as changes in IVTD or ruminal in situ disappearance of DM.