ARS | Publication request: Heat damaged forages: effects on forage energy content

Submitted to: Extension Publications
Publication Type: Other
Publication Acceptance Date: January 24, 2011
Publication Date: March 14, 2011
Citation: Coblentz, W.K., Hoffman, P.C., Undersander, D.J. 2011. Heat damaged forages: effects on forage energy content. Extension Publications. 13:1.

Technical Abstract: Traditionally, educational materials describing the effects of heat damage within baled hays have focused on reduced bioavailability of crude protein as a result of Maillard reactions. These reactions are not simple, but actually occur in complex, multi-step pathways. Typically, the initial step involves the merging of certain plant carbohydrates (often sugars) with protein (amino acids). The undesirable consequence of this reaction is that forage proteins become less digestible to dairy cows or replacement heifers. However, recent work has shown that losses of energy from heated hays are perhaps more important. Net effects of heating on estimates of energy (TDN) decrease in curvilinear patterns with heating. In severely heated hays, reductions in TDN have reached 9 to 12 percentage units, depending on methodology, which constitute an enormous energy loss. Unfortunately, this situation is further compounded because the relationship with heating is not a steady linear decline. Rather, the effects are somewhat ‘front loaded’; in other words, almost all of the losses in TDN are associated with only modest levels of heating. For severely heated hays, there is relatively little additional loss. Overall, energy losses from heated hays have often been ignored in the past, with more educational emphasis placed on reduced bioavailability for CP. This past emphasis is still quite important, but it often results in an understatement of the problem. Spontaneous heating becomes an increasingly likely phenomenon as hay packages become larger; associated losses of energy as a result of heating constitute a serious problem that is (at least) equal in scope to depressions bioavailability for CP.