Studies on ensiling of grass and straw mixtures
The present series of experiments were carried out to determine the effect of i) ensiling straw and grass in various proportions, on chemical composition and nutritive value of silage, ii) homogeneity of mixing of grass and straw on fermentation quality and nutritive value of silage, iii) urea and/or enzyme treatment of straw on chemical composition and nutritive value of grass+ straw silage, and iv) co-conservation of grass-straw on nutritive value of straw. In some experiments feeding value is assessed in the laboratory, and in others by actual feeding trial. In addition a method was developed for determining water in silages using near infrared transmittance spectroscopy. Mixing straw with grass during ensiling diluted crude protein but increased the cell wall constituents. Straw modified fermentation, and more lactic acid and acetic acid were produced in grass+ straw silage than grass-only silage. The fermentation was also affected by the type of grass. The concentrations of ammonia were higher and lactic acid and acetic acid were lower in the silages made from grass/legume than that from only grass. A thorough mixing of grass+ straw is required because ensiling grass and straw in alternate layers increased butyric acid content in silage. Animals ate 22% less dry matter from the silage made in layers than from that made from thoroughly mixed grass+ straw. However, more intensive mixing of grass and silage was not beneficial, as it reduced the digestibility of nutrients and only slightly increased dry matter intake. Increasing the proportion of straw in grass+ straw in a grass+ straw silage reduced intakes of dry matter and digestibility of nutrients. Treatment of straw with urea (60 g/kg straw DM) increased lactic acid content and reduced the contents of cell wall constituents. Urea increased intake and digestibility of nutrients, but enzyme had small effect on intake and digestibility of nutrients by sheep. However, a combination of urea and enzyme was most effective, and increases in the intake of dry matter and digestibility of nutrients were significantly greater in these silages than those treated with either urea or enzyme. The straw composition of cell wall constitutents from straw occurred during ensiling. A method developed for determination of water using NITS is fast and reliable. The model uses the absorbance ratio (OD at 1940 nm/OD at 2284 nm) as a predictor of water in dimethyl sulphoxide which was used to extract water from silages.