Ozone exposure during growth affects the feeding value of rice shoots

Rising tropospheric ozone concentrations have been observed in many Asian countries in recent years. Ozone pollution reduces the yield of agricultural crops but may also affect crop quality. This study aimed at estimating the effect of ozone exposure on feeding quality of rice shoots for ruminant herbivores. Rice plants from two genotypes differing in ozone tolerance were exposed to ozone at a concentration of 120 nl/l for 18 days, and feeding value was determined by chemical analyses and in vitro incubation in rumen fluid. Rice biomass was reduced by an average of 24% in the ozone treatment as compared to the control. Moreover, ozone exposure affected various feed quality parameters. Crude protein content was lower in ozone treated plants (P<0.05). Potential gas production during the in vitro incubation for 96 h also dropped (P<0.01) due to ozone treatment, indicating reduced digestibility of the plant materials. This was explained with an increase in the antinutritive components lignin (P<0.05) and phenolics (P<0.001) due to ozone exposure. An ozone tolerant genotype exhibited a more pronounced increase in phenolics, suggesting that this may constitute a stress defense mechanism. Our results suggest that ozone may affect the feeding value of cereal straws and calls for further research in this direction.