Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2009
Publication Date: 5/15/2009
Citation: Coblentz, W.K., Hoffman, P.C. 2009. Effects of Bale Moisture and Bale Diameter on Spontaneous Heating, Dry Matter Recovery, In-vitro True Digestibility, and In-situ Disappearance Kinetics of Alfalfa-orchardgrass Hays. Journal of Dairy Science. 92:2853-2874.
Interpretive Summary: Spontaneous heating in hay, generally caused by too much moisture in the plant at the time of baling, costs livestock producers in terms of dry matter losses (less hay to feed) and forage quality. Spontaneous heating may also lead to spontaneous combustion and a resulting fire. With conventional small rectangular bales (80 to 100 pounds), a positive linear relationship between moisture content and heating has been clearly established; as moisture increases, so does the amount of heating. But today’s forage producers are using much larger round and square bales, and these larger hay packages have not been studied extensively with respect to spontaneous heating. So we conducted a study to determine if the size of bale (3-, 4-, or 5-foot diameter bales) had an impact on spontaneous heating at different moisture levels. We also measured the amount of dry matter lost and the digestibility of the damaged forages. We observed that large-diameter bales were more likely to exhibit spontaneous heating at relatively low moisture contents (<20%). Also, the amount of feed lost increased linearly with the amount of spontaneous heating in the bales. And the digestibility of the forage decreased at low to moderate levels of heating, but then stabilized thereafter. This study also confirmed that current measures of spontaneous heating are consistently effective indicators of dry matter losses and forage digestibility. This work will encourage forage producers to be more aware of moisture content when producing larger bales, which are less forgiving in terms of spontaneous heating. It also gives livestock producers and nutritionists more confidence when using measures of spontaneous heating to predict its effect on forage quality and digestibility when balancing rations.
Technical Abstract: Alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hay was made in large-round bales from three harvests during 2006 and 2007 to assess the effects of spontaneous heating on 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%. Internal bale temperatures were monitored daily during an outdoor storage period, reaching maxima of 77.2oC (MAX) and 1997 heating degree days > 30oC (HDD) for specific combinations of bale moisture and diameter. Following storage, regressions of DM recovery on HDD and MAX indicated that DM recovery declined linearly in close association with indices of spontaneous heating. For HDD, slopes (P < 0.001) and intercepts (P < 0.001) differed across bale diameters, probably because the greater surface area per kg 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 (r2 = 0.872) when HDD was used as the independent variable. Regressions of DM recovery on MAX also exhibited high r2 statistics (= 0.833), and a common slope (P = 0.830) 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 decay model in which 'IVTD became rapidly negative at <1000 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 (R2 or r2 = 0.820). Changes (poststorage – prestorage) 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 then stabilized thereafter. Both HDD and MAX were excellent predictor variables for both 'Kd and 'DEG; r2 or R2 statistics ranged from 0.788 to 0.921. Measures of spontaneous heating are consistently effective indicators of DM recovery following storage, as well as indicators of concurrent changes in IVTD or in-situ disappearance of DM for heated hays.