THE FEEDING VALUE OF CEREAL STRAWS FOR SHEEP .2. RICE STRAWS

Straws from four rice (Oryza sativa) crops grown in southern New South Wales and two fractions prepared by air separation of one of the straws were described on the basis of chemical composition, grinding energy, in vitro organic matter digestibility (IVOMD) and eating rate by sheep. The intake and digestibility by sheep were also assessed during a 32-day feeding trial. The main differences in characteristics of the six feeds were that one straw contained more cell soluble organic matter (OM) (150 vs. 80 g kg-1 dry matter (DM)), less neutral detergent fibre (NDF) (697 vs. 757 g kg-1 DM), less silica (79 vs. 102 g kg-1 DM), had a lower grinding energy (95 vs. 111 J g-1 DM), had a higher IVOMD (0.52 vs. 0.47) and had a higher acceptability as judged by eating rate (386 vs. 216 g air dry straw h-1). The three other straws and the two fractions of one straw were similar as regards these characteristics, although one of the straws was contaminated with about 0.20 of weeds. The straw which contained more cell soluble OM and that which contained a significant weed component were eaten in greater amounts (480-490 vs. 330-380 g OM day-1) than the other straws. The higher cell soluble OM content was also associated with a higher apparent OM digestibility (0.50 vs. 0.43-0.48). There were no differences between straws in in vivo NDF digestibility or in the rate of disappearance of insoluble DM from nylon bags. Compared with published intake data for other roughages the acceptability of these rice straws was poor. This may have been associated with high silica contents. For example, there was twice as much silica in the leaf fractions as in the stems of these straws, and although leaves were more digestible and physically less resistant to breakdown, there was no evidence of selection for these components. © 1990.