CHEMICAL COMPOSITION OF SILAGES MADE FROM DIFFERENT GRASS GENERA

Abstract

Pure stands of bred and indigenous grasses were established. Each year for 4 years, three 'silage' cuts were taken and the herbages ensiled in laboratory silos. After about 2 months' storage at room temperature the silos were opened and the silages analysed for dry matter, pH, lactic acid, volatile fatty acids and volatile nitrogen. The grasses were analysed for dry matter, crude protein, total water soluble carbohydrate, buffer capacity, acid detergent fibre, nitrate, in vitro digestibility, fructose, glucose and sucrose at time of ensiling. Grass genus had a marked effect on silage quality. The percentage of the silages made from each grass that had pH values of 4.2 or less were as follows: Lolium multiflorum, 97%; Lolium perenne, 72%; Festuca arundinacea, 53%; Poa trivialis, 48%; Holcus lanatus, 26%; Dactylis glomerata, 25%; Agrostis tenuis, 23% and Festuca rubra, 19%. None of the chemical estimations made on the grass correlated well with silage pH, nor did sunshine, rainfall or mean temperature during the 3 days before cutting the grass for silage. The possibility of a quick field test to assess the suitability of a grass crop for ensiling seems remote. Irish permanent pastures contain relatively low levels of Lolium spp (about 6%) and high levels of grasses which are apparently difficult to ensile without a silage additive. Some of the difficulty experienced by farmers in making well-preserved silages from permanent pastures without an additive may be due to the botanical composition of the pastures.