Proteolysis and rumen degradability of protein in alfalfa preserved as silage, wilted silage or hay

First cut alfalfa (Medicago sativa L.) was preserved as control silage without additives (CS), silage with formic acid (FAS), or with sodium methabisulphite (SMS), wilted silage without preservatives (WS), and as moist hay without preservatives (MH) or as traditional hay (DH). Wilting and FA decreased ammonia–N (NH3–N) and free α-amino acid–nitrogen (FAA–N) content compared to CS unwilted silage and SMS. MH and DH had a lower nonprotein nitrogen (NPN) content compared to the silages. The rumen undegraded protein (RUP) (in sacco) in CS and SMS had higher digestibility (solubility) in pepsin/HCl solution compared to the other treatments. Wilting and FA treatment decreased the in sacco soluble fraction of the alfalfa protein compared to CS and SMS. The highest rate of degradation was observed for SMS and DH. The effective degradability of alfalfa protein was higher for CS and SMS and lower for both MH and DH. Rumen protein degradability parameters were highly correlated to NPN or FAA–N content of the forages.