Nitrate poisoning in cattle. 3. The relationship between nitrate intake with hay or fresh roughage and the speed of intake on the formation of methemoglobin.

Abstract

For part 2 see NAR/B 48, 238. 3. In 40 feeding experiments during about 5 years dry or lactating Friesian cows weighing 415 to 670 kg and 3 to 8 years old were given diets of hay, grass pellets, turnips or freshly mown grass in 2 meals daily. During experiments blood from the jugular vein was sampled every 15 min. Cows were induced to increase nitrate intake by being given at least 4 meals of roughage rich in nitrate before blood was sampled. There was a positive relation between nitrate intake and methaemoglobin per cent of total Hb but there were differences within and between different roughages in formation of methaemoglobin. With similar nitrate intake and speed of intake, more Hb was converted into methaemoglobin with hay than with freshly mown grass. That was related to the speed at which the nitrate taken with the roughage was released in the rumen as a substrate for the rumen flora. When hay was soaked in distilled water 80% of the nitrate in the cells diffused into the water within 20 min. With turnip and grass chopped to about 1 cm, 30% of the nitrate diffused into the water within 20 min. (Abstract retrieved from CAB Abstracts by CABI’s permission)