Protein degradation in response to spontaneous heating in alfalfa hay by in situ and ficin methods

Alfalfa forage, field-wilted to 29.9 or 19.7% moisture and packaged in five baling treatments (prestorage control; conventional bales; and laboratory bales made at 1.0, 1.5, and 2.0 times the density of conventional bales), was evaluated for protein degradation characteristics by in situ and ficin assays. Relationships between degradation rates and accumulated heating degree days suggested that these degradation rates are controlled by two conditions. Degradation rates increased concurrently with conservation and minimal heating, primarily because of a large redistribution of highly degradable N that was soluble in prestorage controls, but not in conserved hays. For both methods, this effect appeared to be maximized between 100 and 125 heating degree days. With respect to the in situ method, these effects appeared to be less pronounced, and degradabilities were not affected. After bales accumulated about 125 heating degree days, degradation rates decreased predictably in response to heating by both methods, as did N degradabilities calculated from in situ data. Increases in degradation rates concurrent with con servation and minimal heating appear to be especially important considerations when results of the ficin assay are being interpreted.