Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2010
Publication Date: 7/11/2010
Citation: Coblentz, W.K., Hoffman, P.C. 2010. Effects of Spontaneous Heating on Estimates of Energy from Alfalfa-Orchardgrass Hays Stored in Large-Round Bales. Journal of Dairy Science. 93:479. Interpretive Summary:
Technical Abstract: Using the summative approach to estimate total digestible nutrients (TDN), truly digestible fiber can be estimated from inputs of: i) protein-corrected NDF and acid-detergent lignin (LIG-METHOD); or ii) protein-corrected NDF and 48-h neutral-detergent fiber digestibility (NDFD-METHOD). Our objectives were to assess the relationship between TDN and spontaneous heating, and to describe any differences that may result specifically from the two methods of estimating truly digestible fiber. During 2006 and 2007, mixed alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) hays were obtained from three harvests at the same 8.2-ha research site. Following storage of the hays, both options for estimating truly digestible fiber (LIG-METHOD or NDFD-METHOD) were then used via the summative approach to estimate the total concentrations of TDN (TDN-LIG or TDN-NDFD, respectively). Estimates of both TDN-LIG and TDN-NDFD were related to heating degree days > 30oC accumulated during storage by various regression techniques. Changes (poststorage – prestorage) in TDN-LIG that occurred during storage ('TDN-LIG) were best fitted with a nonlinear decay model in which the independent variable was squared [Y = (11.7 * e-0.0000033*x*x) – 11.6; R2 = 0.928]. For changes in TDN-NDFD ('TDN-NDFD), a quadratic regression model provided the best fit (Y = 0.0000027x2 – 0.010x + 0.4; R2 = 0.861). Generally, 'TDN-LIG was 2.0 to 4.0 percentage units lower (more negative) than 'TDN-NDFD when heating degree days > 30oC exceeded 500. For regressions on maximum internal bale temperature, both 'TDN-LIG (Y = -0.38x + 16.3; r2 = 0.954) and 'TDN-NDFD (Y = -0.25x + 10.2; r2 = 0.848) were best fitted by linear models with heterogeneous (P < 0.001) slopes and intercepts. In general, TDN-NDFD was greater in heated hays than TDN-LIG, largely because the relationship between NDFD and spontaneous heating was poor. In contrast, TDN-LIG declined more rapidly with spontaneous heating, largely because the LIG-METHOD for estimating truly digestible fiber was sensitive to changes in concentrations of both protein-corrected NDF and acid-detergent lignin.