Effect of Heat Treatment of Alfalfa Prior to Ensiling on Nitrogen Solubility and In Vitro Ammonia Production

Two experiments were conducted to assess heat treatment of alfalfa prior to ensiling. In Experiment 1, direct-cut alfalfa (26% DM) was subjected to dry heat (air temperature 400°C) for either 0, 7, 14, 21, or 29s prior to ensiling. Wilted alfalfa (50% DM) was treated similarly for either 0, 5, or 6s. Heat treatment decreased the soluble N content of silage without inducing heat damage. Across all hours of incubation, heating prior to ensiling decreased in vitro NH3 N production in comparison with untreated silage (direct-cut or wilted). Duration of treatment affected NH3 production. Treatment of direct-cut material for at least 14s was necessary to decrease NH3 production in comparison with unheated alfalfa or alfalfa treated for 7s prior to ensiling. Treatment (6s duration) following wilting decreased NH3 production in comparison with heat-treated, direct-cut alfalfa (7, 14, 29s treatments). In Experiment 2, direct-cut alfalfa (36% DM) was subjected to microwave heating for either 0, 30, 60, 120, or 180s prior to ensiling. Heat treatment decreased the soluble N content of silage. Treatment for at least 60s resulted in a further decrease in N solubility. In addition, treatment for at least 60s was necessary to decrease NH3 production. Thus, short-term heat treatment of alfalfa prior to ensiling may be an effective alternative for improving the utilization of silage N in ruminants.