Shoji Uesaka

A Study of Individual Differences in Methemoglobin Formation Caused by Dietary Nitrate Intake

硝酸塩投与に伴なうメン羊血液中のメトヘモグロビン形成における個体差発生の要因を知るため,長期間同一種類の乾草を給与されてきたメン羊6頭を用いて,第一胃内と血液中に既知の硝酸塩,亜硝酸塩を注入した後,経時的に血液中のメトヘモグロビンと,第一胃内容液や血漿中の硝酸,亞硝酸含量を測定し,それより,メトヘモグロビン形成における動物個体間の差異が生じる径路を検討した.その結果,第一胃内に硝酸塩を注入すると,血液中のメトヘモグロビン含量は動物個体間で大きな差異があり,またこれは,第一胃内容液と血漿中の亜硝酸含量にみられる個体差と関連性があるようであった.第一胃内への亜硝酸塩の注入,または血液中への硝酸塩,亜硝酸塩の注入による血液中のメトヘモグロビン含量,第一胃内容液と血漿中の硝酸,亜硝酸含量などの経時的変化における個体差は比較的小さかった.これよりみて第一胃内で硝酸の還元に際して還元中間産物である亜硝酸の状態で第一胃内に留まる量が,同一飼料条件下で飼育された動物個体によって異なり,これがメトヘモグロビン形成にみられる個体差の主要因であると考えられた.また,異なった個体からえた第一胃内容液を用い,in vitroで硝酸塩添加に伴なう亜硝酸蓄積量をみたところ,in vivoでの結果と同様な個本差が認められた.

In Vitro Studies on the Function of the Concentrate in Methemoglobin Formation after Putting Nitrate into the Rumen

乾草を採食している反すう動物に少量の大麦または配合飼料などの濃厚飼料を添加して給与すると,硝酸塩投与後,第一胃内で亜硝酸の蓄積が増し,血液中のメトヘモグロビン含量が多くなるが,濃厚飼料の添加量がさらに多くなると,逆にこれらの成分は著しく少なくなる.この現象の機序を究明するため,濃厚飼料給与の影響を1つは第一胃内で硝酸還元に寄与する微生物にエネルギー源を供給する要因,もう1つは第一胃内容液のpHを変化させることによって硝酸還元の様相を変える要因とに分けて,in vitroで検討した.まず,硝酸塩や亜硝酸塩を添加した第一胃内容液を培養する際,エネルギー源としてでんぷんを添加すると,硝酸の消失は促進されたが亜硝酸の消失はでんぷんの添加,無添加にかかわらず同程度盛んであった.そのため,第一胃内容液の培養液中ではでんぷんが添加された区で,培養1,2時間後に亜硝酸蓄積が比較的多かった.つぎに培養開始時にpHを5.0から7.5の範囲で変化させて培養したところ,硝酸の消失はpH 7.0でもっとも多く,pHが低くなるにつれて少なくなり,とくにpH 5.5,5.0では著しく少なかった.亜硝酸の消失は培養20分後にはpHが5.0から7.5へと高くなるにつれて多かったが,40分後にはpH 5.0のとき30%と少なかった以外は,pH 5.5から7.5の範囲内では93～98%と著しく多かった.そのため亜硝酸蓄積はpH 6.0～7.0のときに多く,pH 5.5以下では著しく少なかった.以上の結果から,少量の濃厚飼料が添加された場合は第一胃内容液のpHはあまり低くならずに,エネルギー源が供給されるので,第一胃内に亜硝酸が多く蓄積するが,濃厚飼料が多給されると,エネルギー源供給の影響よりも,pHが著しく低下するために,第一胃内での亜硝酸蓄積を少なくさせ,さらにこれが直ちに血液中のメトヘモグロビン形成に影響したものと考えられた.

Effects of Kinds and Nutritional Levels of Rations on Methemoglobin Formation by Dietary Nitrate

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.

Effects of Estrogen and Goitrogen on Numbers and Activities of Rumen Micro-organisms

The authors wanted to study on the mechanism of the effects of estrogen or/and goitrogen in cattle fattening from the points of digestion physiology.The effects of these two hormonal substances on numbers and activities of rumen micro-organisms were examined in vivo and in vitro. Diethyl-stilbestrol (DES) was used as an estrogen and methylthiouracil (MTU) as a goitrogen.The effects of DES or/and MTU on the numbers of rumen micro-organisms in sheep were examined twice in vivo with different basal rations but no significant effect was found. The effects of these two hormonal substances on ratios of kinds of rumen protozoa in sheep were examined but no significant result was found either. It was found that when the concentrates and alfalfa pellet were given to the sheep, the number of rumen protozoa increased, and the ratio of Entodinium also increased but the one of Diplodinium decreased, comparing with sheep when the concentrates and hay were given.Using artificial rumen, the effects of DES or/and MTU on performance of cellulose digestion of rumen bacteria in cattle were examined in vitro. But no significant effect was found when the concentration of the hormonal substances was the same with the one which had been used ordinarily for cattle fattening. When the concentration of DES in tube of artificial rumen was over 5mcg/ml, the performance of cellulose digestion of rumen bacteria decreased.Using the artificial rumen, the effects of DES or/and MTU on performance of volatile fatty acids production of rumen protozoa in cattle were examined in vitro but no significant effect was found.From the results mentioned above, the authors guessed that the principal mechanism of the actions of hormonal substances in cattle fattening was not in the part of digestion physiology but in the other part, for example, the part of endocrinology.