Forage may undergo extensive proteolysis during fermentation. The objectives of this study were to determine if treatment of forage with heat can reduce proteolysis during subsequent fermentation. In Experiment 1, direct-cut barley and alfalfa were either microwaved or steamed then ensiled in laboratory silos as were untreated and wilted forage. Silages of microwaved or steamed forage showed marked increase in NDIN and recovery of hot water insoluble N; however, alfalfa silages also had high pH and butyric acid. In Experiment 2, steaming was compared to formic acid and anhydrous ammonia treatments for their ability to prevent proteolysis in alfalfa silages. Steamed and ensiled alfalfa also was evaluated with addition of microbial inoculant or formic acid. Silage of steamed alfalfa had greater NDIN and recovery of precipitable N than controls, formic acid, or ammonia treated silage. There was no difference in precipitable N between formic acid and ammonia treatments. Silage of steam treatment had lower pH than wilted or direct-cut controls, and additives to steamed forage favored a more homolactic fermentation. Additives to steamed forage also increased aerobic stability of the silage. Steamed silage had less aerobic stability than direct-cut silage. Rumen degradability of silage CP and OM from both experiments were evaluated. In Experiment 1, CP degradability of microwaved or steamed silages was 8 to 26% less than unheated silages, but all had similar undegraded CP after incubation for 72 h. In Experiment 2, wilting, steam, formic acid and ammonia treatments had similar, but decreased CP degradability when compared to direct-cut silage. Longer duration heat in Experiment 1 resulted in greater silage protein preservation, and greater decrease in rumen degradability of CP than Experiment 2. / Master of Science