Factors Influencing the Effect of Chemical Treatment on the Nutritive Value of Straw

Abstract

Spray treatment with 4% NaOH in straw DM [dry matter] increased the IVDMD [in vitro dry matter digestibility] by 18.0 percentage units when treated for 3 wk at room temperature. Increasing moisture content in the straw had no beneficial effect on the in vitro digestibility of straw spray treated with NaOH. Ca(OH)2 had very little or no effect on the IVDMD of straw. Increasing time of treatment up to 9 wk had a positive effect on IVDMD of straw spray treated with 2.7 or 5.4% NaOH in DM. A moderate pressure (60 g/cm2) on the ensiled straw increased the IVDMD values by 3-4 percentage units as compared to no pressure. When equal amounts of NaOH (4% of straw DM) was applied, a solution containing 8.5% NaOH tended to give higher in vitro digestibility of the straw than a 17.0% solution. There were no differences in effect between solutions containing 17.0, 25.4 and 34.0% NaOH. A special technique was developed to study the influence of NH3 level, treatment temperature, treatment time and moisture content in the straw on N-content, enzyme solubility and in vitro organic matter digestibility. Although some beneficial effects of increasing the NH3 level from 4.0-5.5% and 7.0% could be seen it can hardly be justified to exceed 4.0% NH3 on straw DM basis. The economical optimum for amount of NH3 lies probably between 2.5-4.0% of DM. The positive effect of increasing treatment temperature was significant, particulary when treatment time was short. When time of treatment was 8 wk or more, the effect of increasing temperature from 16-17 to 24-25.degree. C was uncertain. The interaction between treatment temperature and time was noted. From the present investigation practical experience recommendations were given for treatment time when straw was ammoniated in stacks at varying temperatures. Increasing moisture content in the straw, at least up to 25-30%, had a beneficial effect on the N-content, enzyme solubility and in vitro digestibility of NH3 treated straw. The optimal moisture content is not clear from the present experiments. If the straw is too dry, treatment of the straw with anhydrous NH3 has no effect. Under such conditions aqueous NH3 would be preferable.