Evaluation of the effect of formic acid and level of formaldehyde application before ensiling on silage protein degradability

The effect of the application, before ensiling, of formic acid alone, and together with increasing levels of formaldehyde, on the degradability of the protein of ryegrass and red clover silages has been assessed on the basis of nitrogen solubility in mineral buffer; susceptibility of N to degradation during in‐vitro incubation with either rumen microorganisms, acid pepsin or neutral protease; and N disappearance when the silages were incubated in situ in Dacron bags in the rumen of sheep receiving dried grass. The relative effects of the additives were generally consistent for both crops and with all procedures: formic acid either had no effect or reduced degradability by only a small amount, whereas a mixture of formic acid and formaldehyde was more effective than formic acid alone in protecting protein from degradation, and degradability decreased in a curvilinear manner with increasing levels of formaldehyde application. Absolute values for protein degradability based on buffer solubility and in‐vitro degradation by rumen microorganisms were very similar but lower than those based on digestion with proteolytic enzymes which in turn were lower than those obtained with the rumen in situ procedure. Buffer solubility and in‐vitro incubation with rumen microorganisms also showed much bigger differences between the formic acid‐treated and the formaldehyde‐treated silages than the other methods.