Natural contamination of dietary rice straw with zearalenone and urinary zearalenone concentrations in a cattle herd

The present study was conducted to 1) identify the natural source of feed contamination by zearalenone (ZEN), which was suspected to have caused persistently increased urinary ZEN concentrations in one of our experimental cattle herds, and 2) evaluate the effects of intervention against this source of contamination. As an experimental model, a fattening Japanese Black cattle herd showing persistently increased urinary ZEN concentrations was identified. Urinary ZEN concentrations of cows fed with new rice straw (experimental group, n = 6) vs. cows that continued to feed on the old rice straw (control group, n = 4) were measured at the start (d 1) and at 2 wk (d 14) after the onset of feeding with straw. In addition, the ZEN concentration in feed and water samples was measured by using both the ELISA and HPLC methods. Furthermore, isolation and identification of fungi from rice straw and concentrate feed samples were performed. The urinary ZEN concentration [ZEN (pg/mL)/creatinine (mg/mL) = pg/mg of creatinine] of cows fed with new rice straw was significantly (P <0.05) less (843 pg/mg of creatinine) than that of cows fed with old rice straw (15,951 pg/mg of creatinine). On both d 1 and 14, the ZEN concentrations of old rice straw were greater than those of new rice straw. In addition, fungal colonies were observed in the culture media that was obtained from the old rice straw suspected of ZEN contamination, but not in the culture media from new rice straw or other feed samples. In conclusion, our field trials clearly indicate that the rice straw fed to the cows was naturally contaminated with ZEN, and that the monitoring of urinary ZEN concentrations could prove to be a useful tool for detecting the exposure of cattle to ZEN contamination at the farm level.