異なった飼料条件下で飼育されためん羊における硝酸塩投与によるメトヘモグロビン形成について

Abstract

Three experiments were carried out to study effects of kinds and nutritional levels of rations on methemoglobin formation of wethers by dietary nitrate. In the experiments 1, 2 and 3, three, four and four animals were used respectively. Every animals in the experiment 1 were fed one kind of rations (table 1, Ration 1) for nine days. On the tenth day, 62.4mg of nitrate nitrogen per kg of body weight was administered into rumen by stomach tube just after they had ingested the morning diets. Such treatments, using the other two kinds of rations (table 1, Ration 2 and 3), were conducted at the interval of ten days. Those in the experiments 2 and 3 were fed five and four kinds of rations (table 2 and 3) and were treated equally as in the experiment 1 for 50 and 40 days. After administration of nitrate, nitrite nitrogen concentrations and pH values of rumen fluid and methemoglobin in blood under the different feeding conditions were determined periodically. From the results of these three experiments, it was showed that addition of small amounts of concentrates such as formula feed, cracked barley and soybean meal with timothy hay resulted in more methemoglobin formation than in the case of feeding hay only. It may be due to active nitrite accumulation in rumen fluid under such conditions. However, feeding excess amounts of concentrates, especially those high in energy contents, caused less nitrite accumulation in rumen fluid and methemoglobin formation in blood than those of feeding timothy hay only. Ruminal pH values seemed to decrease when the levels of concentrates in the diets increased. Especially when 30 percent of the diets consisted of concentrates high in energy contents, such as formula feed or cracked barley, pH values went down beyond 5.5. Under such feeding conditions, it was observed that nitrite nitrogen concentration of rumen fluid and methemoglobin in blood were remarkably low.