The effect of heat-treatment and gamma radiation on the composition of unwilted and wilted lucerne silages

Three unwilted and three wilted silages were prepared from lucerne. Unwilted and wilted material was ensiled either without treatment (UWC and WC), after gamma irradiation (UWI and WI), or following heat-treatment and inoculation with Lactobacillus plantarum (UWH and WH). Gamma radiation was from a cobalt 60 source. The UWH material was heat-treated using steam, and WH material was treated with dry heat. At ensiling, irradiated material was considered to be sterile, and heat-treated material had lost 80% of its original protease activity. Fifteen 1-litre silos were prepared for each treatment (90 in total), and three from each treatment were opened after 1, 4, 14, 70 or 200 d ensiling. In irradiated silages, there was no accumulation of organic acids, but water soluble carbohydrate (WSC) concentration was almost double (116 g kg^-1dry matter) that at ensiling. This indicated extensive liberation of WSC from more complex carbohydrates during ensiling. The extent of silage fermentation in heated silages was similar to control silages. The WH silage had a higher proportion of the organic acids as lactic acid relative to the other treatments, possibly as a result of inoculation with L. plantarum. Proteolysis was unaffected by irradiation. However, heat-treatment markedly reduced the extent of proteolysis, particularly in the first four days post-ensiling. Deamination appeared to be related to the type of microbial fermentation rather than to the extent of proteolysis.