Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/25/2010
Publication Date: 7/11/2010
Citation: Coblentz, W.K., Hoffman, P.C., Martin, N.P. 2010. Revisiting Heat-Damaged Protein and Ruminal Degradation Kinetics in Heated Hays. Journal of Dairy Science. 93:478. Interpretive Summary:
Technical Abstract: Previous studies utilizing conventional (45-kg) hay bales have shown that acid-detergent insoluble CP (ADICP), ruminal CP degradation rate (Kd), and rumen degradable protein (RDP) are related to various measures of spontaneous heating during bale storage in simple linear relationships that frequently exhibit relatively high r2 statistics. However, large-round bales often attain much greater maximum internal bale temperatures (MAX) during storage than conventional 45-kg bales, and these greater temperatures may persist for longer durations of time. Our objective was to use regression techniques to relate ADICP, Kd, and RDP with spontaneous heating for 96 large round bales of mixed alfalfa-orchardgrass hay obtained from 3 harvests, and then to compare these responses to the simple linear relationships observed commonly within conventional 45-kg bale packages. Changes in concentrations of ADICP (poststorage – prestorage; 'ADICP) during storage increased with heating degree days > 30oC (HDD), and were best fitted to a nonlinear model [Y = 14.9 – (15.7*(e-0.0000019*x*x)); R2 = 0.934]. A similar quartic response (Y = -0.000053x4 + 0.012x3 – 1.00x2 +35.7x - 470.9; R2 = 0.975) was observed for the regression of 'ADICP on MAX. Changes in Kd during storage ('Kd) were best fitted to cubic models for regressions on both HDD (R2 = 0.939) and MAX (R2 = 0.876), and these changes represented an approximate 50% rate reduction in severely heated hays relative to prestorage controls. Within ranges of heating most commonly encountered under field conditions, changes in RDP during storage ('RDP) declined in mostly linear relationships with HDD or MAX. However, when severely heated hays also were considered, the relationships became cubic (Y = -0.0000000079x3 + 0.000028x2 – 0.027x +1.1; R2 = 0.802) for HDD and quadratic (Y = 0.025x2 – 3.04x + 86.5; R2 = 0.734) for MAX. Generally, responses for ADICP, Kd, and RDP in large-round bales were consistent with the linear nature observed previously within conventional 45-kg bales at low-to-modest increments of heating, but exhibited more complex relationships when heating became more extreme.