Nitrate Metabolism of Microorganisms in the Rumen of Sheep Fed High Nitrate Forages

This study was conducted to investigate the reason why nitrate poisoning in the ruminant occurred more frequently a few days after high nitrate forage feeding on the field. Heavily fertilized green amaranth, Sudan grass, corn soilage and turnip leaves were used as high nitrate materials. After low nitrate forage feeding, sheep were fed chopped high nitrate forages containing 0.33-0.39g of nitrate per 1kg of body weight through rumen fistula twice a day for a week. In the early stage of nitrate feeding no toxic symptoms were observed and maximum amount of nitrite in rumen liquor was rather low in spite of the high nitrate level in the rumen. However, the maximum amount of nitrite increased day by day to reach almost constant level, and methemoglobin in the blood came to 30-40% within six hours after nitrate feeding. Methemoglobinaemia was also observed. More vivid reduction from nitrate to nitrite was observed with rumen microorganisms of the sheep fed high nitrate forages than those of the sheep fed low nitrate forages. From the above results, it was inferred that nitrate poisoning in the ruminant was apt to occur a few days after high nitrate forage feeding due to the adaptation in the reduction of nitrate to nitrite observed with the rumen microorganisms in the change from low to high nitrate forages.