THE CALCULATIONS METHOD USED FOR OPTIMIZING CONDITIONS OF TREATMENT OF BARLEY STRAW WITH CALCIUM HYDROXIDE - EFFECTS OF LEVEL OF CALCIUM HYDROXIDE AND UREA, MOISTURE, TREATMENT TIME AND TEMPERATURE ON IN-VITRODIGESTIBILITY

This study was an attempt to investigate the treatment of barley straw to improve digestibility in vitro: factors considered were the amount s of calcium hydroxide (Ca(OH)2) and urea used, together with other tr eatment conditions (moisture, treatment time and temperature). Chopped barley straw was treated with 25 treatment combinations: different le vels of Ca(OH)2 (20,60, 100 and 120 g kg-1 straw) and urea (15, 45, 75 and 90 g kg-1 straw) using three moisture levels (300, 500 and 700 g H2O kg-1 straw) in duplicate and 'ensiled' in a mini-silo for differen t periods (3, 4, 6, 8 and 9 weeks) at different temperatures (5, 10, 2 0, 30 and 35-degrees-C). Ensiled straw was examined for mould and in v itro organic matter digestibility (OMD) determined. The polynomial app roximation was used to develop contour plots of the response surfaces in the regions of the maximum with an optimum level of Ca(OH)2 and ure a to obtain OMD. The results showed that the optimum moisture content of ensiled straw was 500 g kg-1 and that treatment for 3 weeks produce d satisfactory results. Ensiling treated straw at different temperatur es did not significantly affect digestibility in vitro, but mould inci dence increased with temperature. Increasing the Ca(OH)2 level to 60 g kg-1 straw dry matter (DM) gave linear improvement in digestibility i n vitro. A level of 15 g urea kg-1 straw DM with Ca(OH)2 could be used to prevent mould in ensiled straw.