Effects of maceration of rice straw on voluntary intake and performance of growing beef cattle fed rice straw-based rations

Abstract

Effects of field scale maceration on voluntary intake of rice straw, diet digestibility of neutral detergent fiber (aNDF) and performance of growing cattle were evaluated through chemical, in vitro and animal feeding experiments over a 3-year period. Due to the sequential nature of the study (i.e., a discrete experiment was completed in each year), the method of maceration differed among years. However, in each year, replicated rice fields of approximately 2.4 ha each, which had been managed similarly during growth, were harvested with or without maceration immediately after harvest. While no quantitative measure of maceration was applied in any experiment, the extent of maceration in year 1 was visually judged to be very light, characterized by only a few stem punctures and no longitudinal stem shredding. In year 2, the extent of stem puncture was increased, most internodes were crushed and a small amount of longitudinal shredding had occurred and, in year 3, the amount of internode crushing and longitudinal shredding was extreme. In each feeding experiment, cattle were managed in groups of 8–10 and fed the experimental diets for a 14-day adaptation period prior to weighing on day 0 of the study. Diets consisted of alfalfa hay, concentrate ingredients and rice straw that were fed for ad libitum intake. In general, the chemical composition of the rice straw was typical of California rice straw and, in spite of some differences due to maceration within year, there was no consistent impact on any analyte among years. In each year, the macerated rice straw had a numerically higher calculated metabolizable energy value, but these differences failed to reach statistical significance. The 30 h in vitro digestibility of aNDF in the feces of cattle fed macerated straw was lower (P<0.01) in each study, although the absolute level of aNDF in feces did not differ. Whole tract digestion of dietary aNDF was not impacted by rice straw maceration in experiment 1, was weakly numerically increased in experiment 2 (i.e., P=0.45), and approached statistical significance in experiment 3 (i.e., P=0.07), as the degree of maceration increased. Voluntary dry matter (DM) intake was numerically lower in cattle fed macerated rice straw in each experiment, and both the numerical extent and statistical support for that decline increased from experiments 1 to 3 as the degree of maceration of the rice straw increased, such that the 0.47 kg/d decline in DM intake by feeding macerated straw in experiment 3 was different (i.e., P<0.01). However, body weight gain was not impacted in any experiment and a shift from less efficient to more efficient gain/feed ratio from experiments 1 to 3 failed to reach statistical significance in any year. Maceration, in spite of substantial changes to the physical nature of the rice straw, failed to substantively impact animal performance.