Effects of calcium oxide and calcium hydroxide on the chemical composition and in vitro digestibility of soybean straw

A study was conducted to investigate changes in chemical composition and in vitro digestibility of calcium oxide (CaO) and calcium hydroxide (Ca(OH)(2)) treated soybean straw (SBS). CaO and Ca(OH)(2) were applied to 500 g dry matter (DM) of chopped SBS at rates of 0, 20, 40, 60 and 80 g kg(-1) DM with water (500 g kg(-1) DM) and sealed for 30 days. In vitro digestibilities were determined after incubating samples in buffered rumen fluid for 48 h using ANKOM Daisy(II) Incubators. CaO and Ca(OH)(2) had negative linear effects on the crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) contents. The NDF and ADF concentrations were greatest and least for control groups and high rate (80 g kg(-1)) treated groups (P<0.05), but these concentrations were not significantly different (P>0.05) for control and the low rate (20 g kg(-1)) CaO treatment. Effect of CaO on declining NDF and ADF was greater than Ca(OH)(2), but effect of Ca(OH)(2) on declining ADL was greater than CaO. CaO and Ca(OH)(2) linearly decreased the in vitro digestibility of DM (IVDMD), NDF (IVNDFD) and ADF (IVADFD). The IVDMD, IVNDFD and IVADFD were lowest and highest for greatest rates of treatment and control groups (P<0.05), respectively. There were no significant differences (P>0.05) in in vitro digestibility measurements among control groups and treatments up to a rate of 40 g kg(-1). CaO and Ca(OH)(2) decreased cell wall composition but did not improve in vitro digestibility.