Effect of sodium hydroxide, ozone and sulphur dioxide on the composition and in vitro digestibility of wheat straw

Wheat straw was treated with 5 % sodium hydroxide, ozone, and 5 % sulphur dioxide at 70°C for 72 h, and the effect of treatments on the composition and the in vitro organic matter digestibility (IVOMD) by rumen microorganisms was studied. Ozone and SO 2 solubilised most or all of the straw hemicellulose, converting it into cell solubles, whereas sodium hydroxide exerted a limited effect in this direction. The level of cell solubles increased from 31.8 to 48.2 and 52.2% and that of the reducing sugars from 2.2 to 15.6 and 24.3%, by ozone and SO 2 treatments, respectively. The IVOMD of straw was significantly increased by 80% (from 44 to 80%) with SO 2 , whereas NaOH and ozone improved the IVOMD by only 50% (from 44 to 66%). The initial digestibility (ID at 6 h) suggested to represent substrate fermentability was significantly increased by SO 2 from 7.4 to 29.3 %. In the present study, SO 2 was found to be the most efficient treatment for wheat straw in terms of overall degradability and fermentability. The technological advantage of the proposed treatment lies in the low moisture content (40%) and the moderate temperature required (70°C), conditions which could be attained by solar systems.